Statement on COVID-19 and International Travel

Last content update: June 2, 2022

An Advisory Committee Statement (ACS)
Committee to Advise on Tropical Medicine and Travel (CATMAT)

Table of contents

Preamble

The Committee to Advise on Tropical Medicine and Travel (CATMAT) provides the Public Health Agency of Canada (PHAC) with ongoing and timely medical, scientific, and public health advice relating to tropical infectious disease and health risks associated with international travel. PHAC acknowledges that the advice and recommendations set out in this statement are based upon the best current available scientific knowledge and medical practices at the time of writing, and is disseminating this document for information purposes to the medical community caring for travellers.

Persons administering or using drugs, vaccines, or other products should also be aware of the contents of the product monograph(s) or other similarly approved standards or instructions for use. Recommendations for use and other information set out herein may differ from that set out in the product monograph(s) or other similarly approved standards or instructions for use by the licensed manufacturer(s). Manufacturers have sought approval and provided evidence as to the safety and efficacy of their products only when used in accordance with the product monographs or other similarly approved standards or instructions for use.

Key points/messages

Objectives

This statement is intended to provide guidance for health care providers advising patients on travel in the context of the COVID-19 pandemic.

Recommendations made in this guideline are done within the specific context of health protection for travellers. Policy and regulatory aspects of the COVID-19 response, such as requirements around vaccine passports and quarantine, are outside of the purview of this statement. Travellers should be made aware that factors outside of individual health might have a significant impact on their plans, and that these requirements are subject to change, sometimes with little notice. Travel advisors and their clients should, among other things, regularly verify any travel requirements in place at their destination(s) and for their return to Canada.

Methods

This statement was developed by members of a CATMAT working group (WG), none of whom declared a relevant conflict of interest. The WG and broader committee chose to develop the advice contained herein based on a narrative review of the evidence rather than a formal evidence-based methodologic approachFootnote 1. This reflects, among other things, the need for timeliness and the rapidly changing evidence related to prevention of SARS-CoV-2. The final statement and recommendations were approved by CATMAT.

Epidemiology

Coronavirus disease 2019 (COVID-19) is caused by the novel coronavirus, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), first recognized in Wuhan, China in December 2019. The epidemiology of COVID-19 continues to evolve. Part of this evolution has been the emergence of SARS-CoV-2 variants of concern (VOCs) and variants of interest (VOIs). It is expected that variants will continue to emerge as time goes on. Understanding the impact of these variants on transmissibility, COVID-19 disease severity, and the effectiveness of existing diagnostics, therapies, and vaccines is of crucial importance today, and will remain so into the future.

Up-to-date information on the global epidemiological situation is available through the World Health Organization (WHO)Footnote 2. The WHO COVID-19 Weekly Epidemiological Update also provides a summary on the global epidemiologic picture as well as current and emerging knowledge related to VOCs and VOIs.

Clinical manifestations

The clinical presentation of COVID-19 is highly variable and has been well described elsewhere.

Asymptomatic and pauci-symptomatic infections are common, and play an important role in transmission. However, the prevalence of such infections remains a subject of ongoing discussion/research, with significant heterogeneity between studiesFootnote 3 and for different viral variants. As a general rule, clinical illness is more likely to occur in older persons; indeed, many infections in younger people seem to be unapparent or associated with mild disease. Importantly, transmission is also very common in the days prior to symptom onset, regardless of the intensity of the eventual symptoms.

An area of significant uncertainty and interest is post-acute manifestations of COVID-19. Specifically, some persons, including those with mild illness during primary infection, suffer new or ongoing symptoms or clinical presentations following the acute phase. Current scientific knowledge on post-acute sequelae is limited, and research is ongoing to better understand the long-term effects of infection and possible risk factorsFootnote 4,Footnote 5.

Transmission

The median incubation period of COVID-19 (the time between exposure to SARS-CoV-2 and onset of symptoms) is 5 to 6 days, but can range from 1 to 14 daysFootnote 6,Footnote 7. Incubation periods appear to be slightly shorter for recent variants; for example, Omicron infections tend to have an average incubation period of 3 to 4 days. The primary mode of SARS-CoV-2 transmission is through the respiratory routeFootnote 7,Footnote 8,Footnote 9,Footnote 10. Virus-laden respiratory emissions are produced through actions such as breathing, talking, coughing, sneezing, singing, shouting, or other vocalizations. Transmission can occur through the air, especially in poorly ventilated and highly contaminated environments, including over some distance. Nevertheless, proximity is a key factor in transmission risk. Contact with contaminated fomites (that is, contact with contaminated surfaces) is not considered to be important to the sustainment of pandemic transmissionFootnote 11. This conclusion is based largely on the success of interventions directed only at the prevention of inhaled particles, despite the demonstrated ability of the virus to survive in the environment. Even so, for the individual, the risk of fomite-associated transmission can be greatly reduced by undertaking routine sanitation measures, such as proper hand hygiene and routine cleaning of surfaces. Further, these approaches are considered important for reducing the risk of other travel-associated infections, particularly faecal-oral pathogens that can cause enteric illnesses.

Assessing individual travel associated SARS-CoV-2 risk

There are a litany of considerations that might impact the decision to travel (or not) in the face of the SARS-CoV-2 pandemic. Many are structural, including travel and border regulations, vaccination requirements, and pre-departure testing. This section does not consider these, nor does it consider indirect but very important impacts of individual travel on others, for example the situation where a healthy traveller might act as a SARS-CoV-2 vector for someone who is more vulnerable, or the potential for travel-associated importation of VOCs.

The focus of the present guidance is on individual-level risk assessment related to SARS-CoV-2 and related outcomes. Emphasis is placed on acute and serious COVID-19-related outcomes, such as hospitalization and/or death.

CATMAT acknowledges that there is a constellation of other outcomes of potential concern, including but not limited to long-term post-infection sequelae. These have been reported in children and adolescents as well as adults, both in persons who were very ill with COVID-19 and those who were not. Unfortunately, knowledge and evidence related to such conditions remains inconsistent and somewhat ill-defined, though this is changing as research interest intensifies. Importantly, while severe and acute outcomes are emphasized in this guideline, awareness that infection comes with other risks is something that the clinician and traveller should bear in mind. Further, while the focus of the current guidance is on individual-level risk to the traveller, responsible travel and consideration of the risks posed to destination countries and Canada (through introduction of variants, for example) and more vulnerable contacts should be included in the broader discussion about potential health risks and impacts when considering travel.

CATMAT suggests assessing risk by integrating a traveller-specific exposure assessment with a traveller-specific host assessment. Combined, these yield a risk estimate expressed below as an integrated risk matrix (Table 1). This methodology is generally consistent with approaches applied in other recommendations developed by CATMATFootnote 12,Footnote 13.

Table 1. Risk matrix for international travel in a COVID-19 environment
Exposure Assessment Host Assessment
Low Moderate High Very high
Low Low Moderate Moderate Moderate
Moderate Moderate Moderate High High
High Moderate High High Very high
Very High High High Very high Very high

In Table 1, different factors can contribute to a lower or higher assessment of risk for the individual. For exposure assessments, health advisors should first consider the exposure risk inherent to the destination country or countries, and then may increase (shift down) or decrease (shift up) the exposure assessment as necessary, depending on the anticipated activities and other factors. The host assessment first considers the traveller's age and is adjusted from there based on other individual-level factors; for example, a traveller with diabetes would have their host assessment shifted to the right by one level from their initial age-based level (indicating an increase in the risk of severe SARS-CoV-2 related harms). In a very approximate fashion, each shift by one level represents a 2-4 fold change in risk. Adequate protection from vaccination (see Box 2 for definition) would generally shift the risk level for the traveller to the left by one level (indicating a decrease in the risk of severe SARS-CoV-2 related harms). A summary table of these factors, and how the host and exposure assessment levels may be adjusted accordingly, is provided in Table 6.

The risk matrix and accompanying recommendations are not a surrogate for local, regional, country-level or international travel or public health requirements. Rather they are intended as an adjunct to these, to be used by the health care advisor who is taking on the role of advising patients on travel during the COVID-19 era.

Risk levels from the matrix are expressly linked to recommendations (Table 7). To be clear, these are not GRADE-based recommendations, rather they represent expert opinion based on current knowledge related to SARS-CoV-2.

Finally, the matrix does not consider values and preferences of the traveller. Given that travellers will have divergent COVID-19 risk tolerances, it follows that their acceptance for travel recommendations will vary. It is in this decision-space that travel-related decisions will be made, and where health care providers can help travellers make informed choices.

Exposure assessment

Exposure assessment refers to the likelihood that travellers will be exposed to (but not necessarily infected with) SARS-CoV-2. A thorough review of the planned travel itinerary is necessary to appraise the likelihood of exposure. The baseline for the exposure assessment should be assigned based on the estimated transmission levels at the destination (low, moderate, high, or very high/unknown, see Table 2).

Table 2. Exposure assessment, baseline determined by the estimated SARS-CoV-2 transmission levels at the destination(s), see Appendix for more details and results.
Exposure assessment Estimated SARS-CoV-2 transmission level at destination
Low Low level of SARS-CoV-2 transmission
Moderate Moderate level of SARS-CoV-2 transmission
High High level of SARS-CoV-2 transmission
Very high Very high or unknown level of SARS-CoV-2 transmission

Estimated transmission levels at the destination(s)

The CATMAT Secretariat provided technical support in developing an interim approach for estimating SARS-CoV-2 transmission levels at a destination. This approach uses a combination of indicators of the destination's epidemiological situation (for example, incidence rates, testing rates, percent positivity, trends) and additional situational awareness (see Appendix for more detail and results). The result of this assessment is the categorization of a destination's estimated SARS-CoV-2 transmission as being at a low, moderate, high, very high or unknown level. CATMAT recommends using the estimated transmission level at the destination as the baseline for the exposure assessment.

If several countries are to be visited, then the exposure assessment and resulting recommendations should reflect the entire planned travel itinerary. Recommendations might vary for different segments of the itinerary. In the case of cruise ship travel, CATMAT recommends that the baseline risk of exposure be based on the estimated transmission levels in the country from which the cruise is departing. While it is impossible to ascertain the exact level of transmission in this scenario, the best surrogate for the baseline risk of exposure is the country of departure. If travellers will be disembarking in other countries for significant periods of time, or participating in activities with a higher likelihood of exposure to SARS-CoV-2 while travelling on a cruise, consider applying the same guidance as above regarding multiple itinerary segments. Additional activity-based adjustments to the exposure assessment are suggested for cruise ship travel below.

The baseline risk of exposure may then be adjusted (shifted up or down in the matrix) from the destination-based assessment, based on the factors identified below.

Estimated transmission in the sub-region(s) to be visited

Sometimes, there is subnational variation in transmission estimates for a country. For example, such variability is well monitored and data are easily available in Canada, the United States and the United Kingdom. As appropriate, this information can be applied to refine the exposure assessment. When the epidemiological situation for a sub-region is known to be worse than the transmission levels at the national level, providers may consider increasing the risk level for the exposure assessment by one level. In general, and recognizing this reflects a more conservative approach, CATMAT suggests the opposite not be applied; in other words, the exposure level should not be reduced if there is less transmission in a particular sub-region, relative to the rest of the country.

Duration of travel

Longer duration travel, other things being equal, will be associated with increased cumulative likelihood of exposure(s).

Epidemiologic trends

Where there is information that the epidemiologic picture in a location might be shifting in an important way, for example because of expanding spread of a VOC, consider increasing the exposure assessment by one level. In general, CATMAT currently advises against reducing the exposure level from the initial assessment, based only on promising information.

Types of activities

The types of activities and actions that individuals undertake will also influence the likelihood of exposure to SARS-CoV-2. In general, exposure likelihood increases with an increasing number of contacts, increasing duration of contact, decreasing proximity between individuals, and poor ventilation (in indoor environments). Proper ventilation involves the replacement of indoor air with outdoor air, which helps to reduce the concentration of viral particles, or recirculating air through a high-efficiency particulate air (HEPA) filterFootnote 14,Footnote 15.

For example, attending indoor mass gatherings would be associated with a greater risk of exposure than would hiking with a small group of co-travellers. Likewise, if indoor (or outdoor) gatherings involved actions that were more likely to broadly disseminate virus (for example, singing, shouting, cheering, exertion during exercise) they would be considered to pose a greater exposure likelihood than actions that did not (for example, reading the newspaper, standing quietly in line, shopping in a supermarket).

Table 3 provides a non-exhaustive list of activities characterized by their anticipated exposure level. Where possible, the full spectrum of activities planned by the traveller should be explored. If most or all of their activities are likely to place them at a lower likelihood for exposure, then consider decreasing the exposure assessment by one level from the initial destination-based exposure level. Conversely, the opposite applies if some or many of their activities could place them at relatively higher risk for exposure (i.e. increase the exposure assessment by one level).

Table 3. Types of activities that are considered to be at relative lower or greater likelihood for exposure to SARS-CoV-2
Lower likelihood Medium likelihood Higher likelihood

Lower density outdoor environment. Distancing possible.

Examples: Trekking in a wilderness area, playing golf, individual exercise outdoors, walking in uncrowded areas.

Impact: If most exposure will be of this type, consider reducing the exposure estimate by one level from the destination-based exposure risk (e.g., from high to moderate) [Note: individual events with "high" potential for exposure obviate this, see adjacent]

Lower density indoor activities. Distancing possible, perhaps improved ventilation (can include conveyances).

Examples: Shopping at a mall, attending a small language class, visiting an office building, purchasing groceries, travel on a major/modern airline/aircraft, travel in an uncrowded taxi with open windows, a tour on an uncrowded open-topped bus.

Higher density outdoor activities. Potentially limited distancing.

Examples: Attending an open-air party/concert, visiting a crowded beach, swimming in a public pool, crowded open air bus tours, shopping at a crowded outdoor market, walking in a busy urban environment.

Impact: If most exposure will be of this type, no change to exposure estimate [Note: individual events with "high" potential for exposure supersede this, see column to the right]

Higher density indoor activities. Often limited distancing, many people, limited ventilation (can include conveyances), actions that facilitate virus dispersal (e.g., singing, shouting, cheering, loud talking, exertion during exercise).

Examples: Travelling on a cruise ship, eating at a buffet, attending a large conference, attending a large indoor music concert, attending a sports event at an indoor stadium, attending a large indoor service, going to a busy indoor bar/restaurant, attending an indoor fitness class/crowded gym, travel in a crowded and closed and/or poorly ventilated conveyance (e.g., a local bus/minibus).

Impact: If there is potential for a significant amount of exposure of this type (even if it reflects a single event, e.g., attending a "crowded" indoor wedding), consider increasing exposure estimate by one level from the destination-based exposure risk (e.g., from moderate to high)

Conveyances

Evidence of the likelihood and extent of SARS-CoV-2 transmission on conveyances is generally limited. Much of the available research pertains to air travel and transmission on aircrafts. Current evidence seems to indicate that the risk of SARS-CoV-2 transmission on aircrafts is generally lowFootnote 16. However, substantial heterogeneity in study designs and low quality of evidence across many published studies has been noted. Furthermore, attributing in-flight transmission is complicated by the possibility of alternative opportunities for exposure including those related to air travel, but not while on-board the aircraft (e.g. waiting spaces such as security checkpoints and boarding gates).

Cruises are another conveyance that pose a potentially important public health challenge. Certain characteristics associated with cruise trip travel lend themselves to increased transmission or outbreaks of infectious respiratory and diarrheal diseasesFootnote 17,Footnote 18. Outbreaks of SARS-CoV-2 on cruise ships have been documented throughout the pandemic, though the most studied remain the outbreaks occurring on the Diamond Princess and Grand Princess cruises early in February 2020Footnote 17,Footnote 19,Footnote 20. The generally closed environment of cruise ships, coupled with close contact among the population on board and potentially suboptimal ventilation systems, creates favourable conditions for SARS-CoV-2 transmission. Furthermore, medical facilities and services on cruise ships may vary widely. Responses to outbreaks on cruise ships may result in delays in disembarkation and transfer to adequate medical services if required. Medical advisors should ensure that travellers are made aware of these additional risks. Additionally, health advisors should consider increasing the exposure assessment by one level from the destination-based exposure risk for cruise ship travel.

Clusters and outbreaks have also been documented in association with other forms of transportation (for example, crowded unventilated buses have been associated with outbreaks), though evidence is limitedFootnote 21,Footnote 22. Nevertheless, factors that may exacerbate the risk of transmission in indoor spaces can also be applied to the context of conveyances. Characteristics of the environment, and how individuals interact within that environment, can influence opportunities for exposure (e.g. density of contact, duration spent on the conveyance, size/layout of the space, use of public health measures such as masking, and quality of ventilation). Measures to reduce opportunities for exposure, where feasible to implement, can focus on these factors.

Judgement

CATMAT acknowledges that while the baseline for the exposure assessment is based on quantitative estimates of transmission level, the assessment is then adjusted based on various qualitative factors, and should always be applied respecting the specific context. Judgement, common sense, and flexibility are required. For example, travelling to an area where there is virtually no SARS-CoV-2 transmission should not normally require further activity-based adjustments to the exposure assessment. Conversely, engaging in activities with a lower likelihood of exposure to SARS-CoV-2 should not necessarily prompt a decrease in the exposure risk assessment if travel will be to an area experiencing a surge in transmission. Indeed, in the latter situation the health care advisor might consider increasing the exposure assessment by one level based on the shift in the epidemiologic picture. Box 1 provides examples of exposure assessments.

Box 1. Examples of exposure assessments

Exposure likelihood decreased from the initial destination-based exposure assessment

A couple is travelling to Country A by air for a two-week trekking trip. They plan to stay in the country's populous capital for several days, after which they will join a cohort of travellers (from a low transmission country) that will remain together for the trek. Accommodations will not be shared with others in the travel cohort, but there might be shared indoor meals.

In this example, the country is considered to have a high level of SARS-CoV-2 transmission. The planned activities involve actions that could include increased exposure likelihood, particularly to other participants on the tour. The tour group effectively comprise an imperfect cohort (some mixing with local populations) however, much of the trip will be spent outside in a "low density" environment.

Air travel in a modern commercial aircraft is not considered a higher likelihood exposure.

Consider decreasing the exposure assessment by one level to moderate, if the large majority of exposure will be with others in the low risk travel cohort, in a low density setting and there are no planned activities with a higher likelihood of exposure (see Table 3).

Exposure likelihood increased from the initial destination-based exposure assessment

A family is travelling to Country B to visit relatives. They plan to attend indoor sporting events and expect to take advantage of the largely re-opened economy to enjoy themselves at venues such as restaurants and amusement parks.

In this example, the country is considered to have a moderate level of SARS-CoV-2 transmission. The planned activities involve actions that could include increased exposure likelihood.

Consider increasing the exposure assessment by one level to high.

Host assessment

Host assessment refers to the likelihood that travellers will suffer significant SARS-CoV-2 infection-related harms.

Vaccination status

Setting aside host-based predispositions towards serious harm if infected, the most important modifiable risk factor for protection against COVID-19 is vaccination. In this respect, the current evidence suggests that COVID-19 vaccines approved and used in Canada provide moderate to high levels of protection against severe diseaseFootnote 23. Protection against symptomatic infection has also been shown, but the degree and duration of protection appears to be more variable, potentially impacted by factors such as age, timing of dosing intervals, and in the context of VOCsFootnote 23.

For most persons deemed to be adequately protected through vaccination (see Box 2 for definition), CATMAT suggests that the host assessment be reduced (shifted to the left) by one level, from the baseline age-based assessment (see Table 4).

This would mean, for example, a person otherwise considered at high likelihood of significant SARS-CoV-2 infection-related harms based on the host assessment, would be considered at moderate likelihood, if adequately protected by vaccine.

Box 2. Defining adequate protection, for the purposes of the travel risk assessment

For the purposes of risk assessment, an individual may be adequately protected by vaccine if:

  • They have received a complete series of COVID-19 vaccine, according to recommended schedules, and any additional/booster doses (if eligible).

By COVID-19 vaccine, CATMAT is referring to any COVID-19 vaccine products authorized for use in Canada according to recommended schedulesFootnote 24 or a non-Health Canada authorized vaccine (one or two doses) followed by the provision of any additional doses of mRNA vaccine (or other acceptable Health Canada authorized vaccine), in accordance with recommendations from PHACFootnote 25. Medical advisors should keep apprised of the latest guidance from NACI/PHAC, as considerations for adequate protection may evolve over time.

The term adequately protected by vaccine used in this document for the purpose of travel risk assessment may not be entirely consistent with the vaccination requirements in other countries, nor with requirements for exemption from border measures such as quarantine upon return to Canada. When advising patients on travel, providers should apprise travellers of this distinction, and that they will need to monitor the requirements for vaccination at their destination(s) and for their return to Canada.

CATMAT recommends that NACI guidance on the use of COVID-19 vaccines be followed, including for travellers. However, there are unique travel-related circumstances related to vaccination. These are considered in the sections below.

In addition to protection against disease, vaccination may act to reduce transmission, both by preventing infection altogether and by reducing onward transmission in the case of breakthrough infectionsFootnote 26. This remains an area of active research interest, with greater uncertainty in light of VOCs such as Omicron, for which COVID-19 vaccines appear to have substantially lower vaccine effectiveness against symptomatic infectionFootnote 23. Nevertheless, letters for exemption from vaccination are discouraged. This is not only for the safety of travellers and their companions, but also as this represents a risk of importation into the destination country.

Variants of concern (VOCs)

At the time of writing, and recognizing that there are many unknowns related to vaccine performance against VOCs, the evidence is suggestive that a complete vaccine series with a Health Canada authorized COVID-19 vaccine provides a high level of clinical protection against severe disease associated with most VOCs. As this is an evolving area of research, NACI guidance on use of COVID-19 vaccines should continue to be monitored, as the epidemiology and evidence pertaining to VOCs and COVID-19 vaccines changesFootnote 23,Footnote 24.

Complete or partial series

CATMAT acknowledges that a partial vaccine series provides substantial protection against earlier SARS-CoV-2 strains, such as the ancestral strain, as well as the Alpha variant (previously called B.1.1.7). However, protection against VOCs such as Delta and Omicron has been significantly less reliable, particularly regarding symptomatic illness and asymptomatic infection, as well as the ability to prevent transmission if infectedFootnote 23. For this reason, for the sake of simplicity, and in recognition that the likely policy framework for many/all jurisdictions will be based on receipt of a complete vaccine series, CATMAT suggests that the host assessment only consider persons as adequately protected by vaccine if they meet the criteria outlined in Box 2.

How to advise travellers who have been confirmed to be previously infected with SARS-CoV-2

Current evidence suggests that individuals known to be previously infected with SARS-CoV-2 are likely to have at least moderately durable protection, for six months or longer, against the SARS-CoV-2 variant associated with the original infectionFootnote 27,Footnote 28. There is less certainty about protection against VOCs. For VOCs prior to Omicron, there is some evidence to suggest that past infection offers good protection from re-infection, though this decreases over time. Furthermore, this protection is increased through vaccinationFootnote 23. Previous infection alone appears to provide a lower degree of protection against subsequent infection from Omicron; when combined with vaccination, this protection appears to be somewhat bolsteredFootnote 23,Footnote 29.

NACI continues to recommend that COVID-19 vaccines should be offered to individuals with previous SARS-CoV-2 infection without contraindications to the vaccineFootnote 23,Footnote 29. CATMAT endorses this guidance, and further suggests that such persons not be considered as adequately protected for the purposes of the host assessment based on evidence of previous infection. Vaccination timing for individuals with a previous SARS-CoV-2 infection should be as recommended by NACI.

For the purposes of the travel risk assessment, CATMAT does not consider individuals with previous SARS-CoV-2 infection who have received only a partial series of Health Canada authorized COVID-19 vaccine to be adequately protected in the host assessment. In other words, advisors would not decrease the host assessment (i.e. shift to the left in the risk matrix) by one level for these individuals. Previously infected individuals with a partial series should continue to be advised to complete their COVID-19 vaccine series, according to recommended schedulesFootnote 29, prior to travel.

Evaluating immunity in travellers who are not vaccinated according to recommended schedules or, who may have been previously infected, is complex and difficult at this time. Risk of severe disease if infected likely falls somewhere in the range of being up-to-date in vaccination (as in, according to recommended schedules), and being unvaccinated with no previous infection. The decision to consider these individuals as not being adequately protected in the host assessment is a reflection of these uncertainties.

This guidance will continue to evolve based on evidence of clinical protection. At this time, comparative vaccine effectiveness data between these groups (one dose in previously infected individuals compared to a complete series in individuals without prior infection) are lacking, and protection against most VOCs is uncertainFootnote 23.

Vaccination and quarantine/testing requirements in Canada

The definition of what constitutes adequate protection by vaccine, that is applied in this guidance, may differ from that which will be applied to policy around travel and quarantine requirements or other border measures for vaccinated individuals departing from or returning to Canada. Travellers should be made aware of the current requirements in Canada, including relevant provincial/territorial and local legislation, regulations, and policies, and that these could change during their travel period.

Host "risk" factors

Age

Age, as a risk factor, has the most profound impact on the likelihood of developing the most serious COVID-19 outcomes (for example, ICU admission, death). Importantly, age is confounded with other risk factors, particularly co-morbidities such as diabetes, obesity, and cardiovascular disease, such that the independent impact of age is reduced in adjusted analysesFootnote 30,Footnote 31,Footnote 32. Nonetheless, public health authorities (including Canadian at the federal, provincial, and territorial levels) use age as a fundamental baseline for assessing host vulnerability to, and consequent recommendations for the prevention of, COVID-19; CATMAT has adopted this approach (see Table 4).

Though presented as finite groupings in the host assessment table, there is also within group variation in the likelihood of severe disease, with the likelihood of severe outcomes being generally higher among older age groups, relative to younger ones (for example, the likelihood of severe disease is substantially lower among healthy 30-year-olds as compared to healthy 59-year-olds). Given the evolving evidence regarding risk of severe outcomes from COVID-19 in infants under 1 year, this pediatric population should be excluded from the age-based risk assessment. Health professionals should consider these limitations when advising individuals travelling with children under 1, and take care to remind travellers that travel with infants may be higher risk for several reasons, including lower immunologic development and experience in this population and access to appropriate care and treatment should they become ill (COVID-19 related or otherwise).

Table 4. Host assessment, baseline level determined by age (in years) at the start of travel
Host Assessment
Low Moderate High Very high
Age (in years) at start of travel 1 to 29 30 to 59 60 to 79 80+

In general, if a person is considered to be adequately protected by vaccine (see Box 2), CATMAT suggests that the host assessment be reduced (shifted to the left) by one level, from the baseline age-based assessment. For persons with identified risk factors (see Table 5), increase the host assessment (shift to the right) by at least one level from the age and vaccination-based level.

Children less than 5 years of age

At the time of writing, none of the COVID-19 vaccines currently authorized in Canada are indicated for use in children less than 5 years of age. Barring any pre-existing medical conditions, this group is considered to be at low risk for severe COVID-19 associated outcomesFootnote 33,Footnote 34,Footnote 35. Even though children are at low risk of severe outcomes, even if unvaccinated, they may act as reservoirs for transmission. Furthermore, the risks of prolonged symptoms (also referred to as "long COVID") following infection are not well quantified in children at this time. Hence, care should be taken to protect children and others around them from infection through assiduous use of personal preventive measures, when in situations with higher transmission risk, such as crowded or poorly ventilated settings. In the absence of vaccination, recommendations as outlined in Table 7 continue to apply to children as well as adults. Where mixed age groups are travelling together, vaccination of those who are eligible acts as an important adjunctive measure in providing some indirect protection to younger children and any other groups that are unable to be vaccinated or, that will not derive the same degree of individual protection from vaccination.

Though many gaps remain in understanding COVID-19 in children, current evidence suggests that risk factors for severe disease include underlying medical conditions such as type 1 diabetes, neurological conditions, chronic pulmonary diseases other than asthma, cardiac and circulatory congenital anomalies, obesity, and immune dysregulation associated with Down Syndrome and other immunocompromising conditionsFootnote 36,Footnote 23,Footnote 37; some of which are similar to those risk factors observed in adults (see Table 5). As such, CATMAT recommends that the same approach (to increase the host assessment level from the initial age-based assessment based on presence of other risk factors) be applied when assessing children.

In addition to the aforementioned health considerations, families travelling with children should also be aware that countries may have differing requirements for children under 5 years of age, and in some cases, the same entry, quarantine, and testing requirements may apply as for other unvaccinated travellers.

Other risk factors

The impact of other risk factors on the most serious COVID-19 outcomes is an area of ongoing investigation with a plethora of available peer-reviewed and pre-peer review evidence available. A list of underlying medical conditions associated with more severe COVID-19 disease is available in COVID-19 signs, symptoms and severity of disease: A clinician guide, produced by the Public Health Agency of Canada. In general, the risk of more severe disease increases with the number of medical conditions.

Table 5. Underlying medical conditions associated with increased risk for severe outcomes from COVID-19 (extracted from COVID-19 signs, symptoms, and severity of disease: A clinician guide from PHAC)
Increased risk of severe outcomes from COVID-19 (hospitalization/mortality)

Medical conditionsFootnote a :

  • asthma (moderate to severe)
  • cancer
  • chronic kidney and end-stage disease
  • chronic lung diseases
  • cystic fibrosis
  • dementia or other neurological conditions
  • diabetes (type 1 or type 2)
  • Down syndrome
  • epilepsy
  • heart conditions
    • such as heart failure, coronary artery disease, cardiomyopathies or hypertension
  • HIV infection
  • immunocompromised state
  • interstitial lung disease
  • liver disease
  • motor neuron diseases
  • overweight and obesityFootnote b
  • pregnancy
  • pulmonary hypertension
  • sickle cell disease or thalassemia
  • smoking, current or former
  • solid organ or blood stem cell transplant
  • stroke or cerebrovascular disease
  • substance use disorders
Footnote a

The conditions provided here may not reflect the most up-to-date guidance. For the most current list of conditions, health care advisors should also refer to COVID-19 signs, symptoms, and severity of disease: A clinician guide.

Return to footnote a referrer

Footnote b

Overweight = body mass index (BMI) > 25 kg/m2 but < 30 kg/m2), obesity (BMI ≥30 kg/m2 but < 40 kg/m2), or severe obesity (BMI of ≥40 kg/m2).

Return to footnote b referrer

CATMAT suggests that the risk factors identified in the PHAC guidance be used to modify the host assessment in much the same way as was used for the exposure assessment. However, for the host assessment, the adjustment will be unidirectional (as in, it may only result in a shift towards a higher risk level). Generally, CATMAT recommends increasing the host risk assessment (shifting to the right) by at least one level if the traveller has any of the underlying medical conditions identified in Table 5. It is recognized that this is a conservative approach, as some or all of the risk associated with the other identified individual risk factors is likely already factored into the age-based groupings.

In the situation that the health advisor considers the traveller to be especially vulnerable to COVID-19 (independent of age), such as due to the presence of multiple risk factors or particularly severe medical conditions, consider shifting the host assessment to the right by two levels (indicating a larger increase in the risk of severe SARS-CoV-2 related harms). Box 3 provides examples of host assessments. Furthermore, a list of conditions under which individuals would be considered moderately or severely immunocompromised can be found in the COVID-19 vaccine chapter of the Canadian Immunization Guide.

Due to the paucity of evidence on the efficacy and effectiveness of vaccination in preventing severe outcomes from COVID-19 among populations with known immune suppression, CATMAT recommends a conservative approach in applying the risk matrix assessment to these individuals. Many or all will derive some protection from vaccination and it is strongly advised that NACI guidance on the use of COVID-19 vaccines in this population continue to be followed and closely monitored as the evidence evolves on how to optimize protection in this diverse populationFootnote 23,Footnote 38.

If the traveller has any of the conditions under which individuals would be considered moderately to severely immunocompromised, found in the Canadian Immunization Guide, CATMAT maintains the recommendation to increase the host risk assessment (shift to the right) by at least one level. For immune suppressive conditions, or for immune suppressing medications, the clinical implications will vary significantly among travellers and should again be subject to individual assessments and clinical discretion. The effectiveness of COVID-19 vaccines is not well known and may be reduced in these individuals. As such, immune suppressed travellers may be at risk both due to their underlying disease and because their protection from vaccine may be reduced. Accordingly, providers may consider during an individual assessment whether the host risk assessment should be increased (shifted to the right) by more than one level. In some cases and based on consultation with a medical expert, it may be appropriate to exercise caution, and treat these individuals in the host assessment as not being adequately protected by vaccine, regardless of their actual vaccination status. Though not specific to COVID-19 vaccines, health care advisers may also refer to Immunization of immunocompromised persons in the Canadian Immunization Guide, Part 3 - Vaccination of Specific Populations, for further discussion and considerations regarding immunization of immunocompromised individuals.

Box 3. Examples of host assessments

Likelihood of severe outcomes decreased from the initial age-based host assessment

A 70-year old individual who is healthy and without identified risk factors is planning to travel. The patient has received a complete series of COVID-19 vaccine, with a product authorized for use in Canada and thus, is considered adequately protected (see Box 2).

This patient is at increased risk for severe COVID-19 if infected, by virtue of their age. They should be carefully screened for other risk factors. If none are identified, due to their vaccination status, consider reducing their host assessment by one level from their aged-based risk (moving them from high to moderate).

Likelihood of severe outcomes increased from the initial age-based host assessment

A 40-year old person with Down syndrome is planning to travel. The patient also has diabetes, and is adequately protected by vaccine (see Box 2 for definition).

This patient is at increased risk for severe COVID-19 if infected based on two identified underlying medical conditions. Given this, consider adjusting the host assessment by two levels based on risk factors. However, as the individual is adequately protected by vaccine (which can reduce the risk by one level), full adjustment will result in an increase of only one level, from moderate to high.

Access to adequate medical care

Travellers, particularly those individuals deemed to be at moderate or high risk of severe outcomes who must travel, should also consider the availability and potentially high cost of adequate medical services in the destination country, should they become infected and require urgent care. Travellers may experience difficulties acquiring transportation if they must be transported elsewhere to receive suitable care. Furthermore, any travel and treatment costs incurred might not be covered by travel-specific insurance.

Furthermore, should travellers become infected while travelling, they may experience delays in returning home to Canada, which may be costly. In the scenario of poor or limited access to these services, health care professionals advising these individuals may consider recommendations from a higher risk category, where appropriate.

Integrated risk assessment

Combining the exposure and host assessments yields a risk assessment matrix as shown in Table 1. Risk matrix for international travel in a COVID-19 environment. Host and exposure assessments consider a variety of factors (see above) and risk levels can be adjusted (as in, increased or decreased) based on the attributes of the traveller and their travel plans (for example, vaccination status, risk factors for severe disease, and exposure in environments conducive to transmission). A summary table of these factors and how the host and exposure assessment levels may be adjusted accordingly is provided in Table 6.

Table 6. Summary of traveller (host) attributes and travel plans (exposures), and their application in the risk matrix
Exposure assessmentFootnote a,Footnote b,Footnote c Host assessmentFootnote d,Footnote e

Consider increasing exposure assessment by at least one level, if:

  • The epidemiological situation for a sub-region is known to be worse than the national level transmission.
  • There is a shifting epidemiological situation that could increase risk of SARS-CoV-2 exposure (e.g. increasing spread of VOCs).
  • Some/many activities in the planned itinerary place the traveller at a relatively higher risk for exposure (see Table 3).

Consider increasing host assessment by at least one level, if:

  • The traveller has any of the medical conditions listed in Table 5 or, is otherwise assessed by a medical professional as being at increased risk of severe outcomes (e.g. due to other immunosuppressive conditions)Footnote f.
  • The traveller is at moderate or high risk of severe outcomes, and will have poor or limited access to health care services at their destination.

Consider decreasing exposure assessment by one level, if:

  • Most/all activities in the planned itinerary place the traveller at a lower likelihood for exposure (see Table 3).

Consider decreasing the host assessment by one level, if:

  • The traveller is adequately protected by vaccine (see Box 2 for definition)Footnote g.
Footnote a

Exposure assessment refers to the likelihood that travellers will be exposed to (but not necessarily infected with) SARS-CoV-2.

Return to footnote a referrer

Footnote b

Baseline for the exposure assessment will be assigned based on the estimated transmission levels at the destination(s).

Return to footnote b referrer

Footnote c

The exposure assessment, while based on quantitative estimates of transmission level, is qualitative, and should always be applied respecting the specific context. Judgement, common sense and flexibility are required.

Return to footnote c referrer

Footnote d

Host assessment refers to the likelihood that travellers will suffer significant SARS-CoV-2 infection-related harms.

Return to footnote d referrer

Footnote e

Baseline level for the host assessment is based on the age (in years) at the start of travel (see Table 4).

Return to footnote e referrer

Footnote f

If the traveller is considered to be especially vulnerable to COVID-19 (independent of age), e.g., due to multiple or particularly severe risk factors, consider increasing the host assessment (as in, shifting right in the matrix) by two levels. A list of conditions under which individuals would be considered moderately or severely immunocompromised can be found in the COVID-19 vaccine chapter of the Canadian Immunization Guide.

Return to footnote f referrer

Footnote g

The effectiveness of current vaccines in certain immune suppressed individuals is currently unknown and may be suboptimal. To account for uncertainty in the effectiveness of current vaccines in these travellers, in some cases and based on consultation with a medical expert, it may be appropriate to exercise further caution, and treat these individuals in the host assessment as not being adequately protected by vaccine, regardless of their true vaccination status.

Return to footnote g referrer

Other considerations

Vaccination outside of Canada

In general, CATMAT advises against receipt of vaccines not authorized in Canada, or offered in international locations where vaccine storage and handling may not reflect Canadian standards. Rather, emphasis should be placed on receiving a complete series with (a) vaccine(s) authorized for use in Canada before leaving Canada. This recommendation reflects, among other considerations: uncertainty related to the effectiveness or safety of products that are not authorized for use in Canada; uncertainty about the robustness of vaccination protocols (including post-vaccination monitoring and management of acute adverse events); and the ease of vaccination in Canada. Furthermore, given the time required to mount an immune response between doses, and the recommended intervals between doses to optimize immune response to the vaccineFootnote 23, for many travellers the benefits of vaccination will not accrue until after travel has been completed.

For some travellers, for example those who will be outside of Canada for a longer period of travel (more than a month) and cannot complete a series before departure, consideration should be given to receipt of vaccine outside of Canada. This may include children who become eligible for vaccination while abroad, and will remain outside of Canada for more than a month. This is the less preferred option, compared to pre-departure completion.

Assuming vaccination outside of Canada is being considered, then the factors mentioned above should be considered as part of the risk-benefit analysis. If the traveller decides to pursue vaccination outside of Canada, then they should be advised to opt for a vaccine product that is authorized for use by Health Canada and follow NACI guidance. If this is not possible, then preference is for vaccines that have met the necessary safety and efficacy criteria of the WHOFootnote 39. In addition to vaccines authorized for use in Canada, additional COVID-19 vaccine products have been given authorization for emergency use by the WHO. However, not all of these products will necessarily meet the same efficacy standards as has been demonstrated for Canadian-licensed products, nor will they necessarily meet regulatory requirements for country entry, quarantine modification, etc. Travellers who receive a COVID-19 vaccine product that is not currently authorized for use in Canada should also be made aware that additional doses of mRNA vaccine may be offered upon their return to Canada, in accordance with current guidance from the Public Health Agency of Canada, in order to optimize protection.

Serologic testing

Serologic testing is not routinely recommended for travellers. Commercial tests are increasingly available, and are generally of two types. Antibodies to the nucleocapsid of SARS-CoV-2 occur during natural infection to a variable degree, and after vaccination with some vaccines that use whole virus as an antigenFootnote 40. Antibody to the spike protein occurs after both infection and vaccination. In general, high titres of neutralizing antibodies are relatively predictive of protection against a given strain of virus, however an accurate correlate of protection has not been determined. Cell mediated immunity appears to also be an important factor in vaccine protection, but tests are not standardized or commercially available. Commercial serologic kits have been of highly variable accuracy, correlate only partially with neutralizing antibody assays, and a given assay may not indicate protection against a given viral variant. Therefore, while the absence of antibody to spike protein in a recently vaccinated individual might raise concerns regarding vaccine response and protection, the problems with sensitivity and specificity, and lack of validation as good correlates of protection, render testing of little practical utility in the individual traveller.

Irrespective of their utility, travellers should be aware that countries may still choose to use serologic testing as part of the regulatory requirements for entry or in determining exemptions to other border measures such as quarantine.

Recommendations

It should be made clear to any individuals planning to travel outside of Canada that they may often be increasing their risk of COVID-19 by travelling, even while taking the recommended precautions. This should be factored into any discussions between practitioners and their patients, when considering travel. Recommendations based on the integrated risk assessment are provided in Table 7. However, the following broad guidance applies to all individuals intending to travel outside of Canada:

Table 7. Recommendations for travellers based on the integrated risk assessment
Integrated risk assessment Recommendations
Low Comply with all local COVID-19 regulations and practice basic hygiene principles applicable to all situations.
Moderate Recommendations as per low risk, as well as non-medical public health measures (mask wearing, physical distancing), if not already specified by local regulations at the destination(s).
High Recommendations as per moderate risk as well as limiting exposure length to as short as reasonably possible / choosing alternate activities when possible.
Very high Recommendations as per high risk and consider deferring travel plans altogether. If travel must occur, recommend testing during travel based on contacts or symptoms, and reducing exposure to high density environments and high risk contacts after return to Canada. In a group setting with increased risk of transmission, consider the use of rapid testing.

Acknowledgements

This statement was prepared by the COVID-19 Working Group: Libman M (Chair), Lagacé-Wiens P, Boggild A, Vaughan S, Lee J, Bui Y, Schofield S, Rossi C, Tunis M and Jensen C (National Advisory Committee on Immunization Secretariat), and Farmanara N (CATMAT Secretariat) and was approved by CATMAT.

CATMAT would like to acknowledge the technical and administrative support from the Centre for Border and Travel Health at the Public Health Agency of Canada for the development of this statement.

CATMAT members: Libman M (Chair), Lagacé-Wiens P, Boggild A, Bui Y, Vaughan S, Greenaway C, Acharya A, Lee J, Bogoch I, Plewes K.

Liaison members: Angelo K (Centers for Disease Control and Prevention), Pernica J (Association of Medical Microbiology and Infectious Disease Canada), Viel-Thériault I (Canadian Paediatric Society).

Ex officio members: Marion D (Canadian Forces Health Services Centre, Department of National Defence), Plamondon M and Kerr P (Biologics and Radiopharmaceutical Drugs Directorate, Health Canada), Rossi C (Medical Intelligence, Department of National Defence) and Schofield S (Pest Management Entomology, Department of National Defence).

Conflict of interest

None declared.

Appendix: Estimated SARS-CoV-2 transmission levels by destination

Description

This appendix summarizes the estimated SARS-CoV-2 transmission levels at a destination. Destinations are categorized as either having low, moderate, high, very high or unknown levels of transmission based on several indicators. Some of the indicators that the assessment process considers include:

If there are no, or insufficient data available to estimate the level of SARS-CoV-2 transmission for a particular destination, they are included in the unknown transmission category. From a functional perspective, these destinations should be categorized as Very high in the exposure assessment.

Considerations

While this appendix will be updated regularly, it is possible that it will not reflect the most up-to-date information on the level of SARS-CoV-2 transmission at a particular destination. Furthermore, while adjustments will be made where possible, this approach relies on reported COVID-19 case data. Data limitations, such as underreporting of cases, may result in an underestimation of transmission levels for a particular destination. Results are presented at a country/destination level, and as such do not account for sub-national variation in transmission.

Appendix: Estimated SARS-CoV-2 transmission levels by destination
Date of assessment: August 29, 2022
Estimated SARS-CoV-2 transmission levels Country/destination
Low level of SARS-CoV-2 transmission
  • Antarctica
  • British Virgin Islands
  • Cabo Verde
  • China
  • Equatorial Guinea
  • Eritrea
  • Falkland Islands
  • Kiribati
  • Macau
  • Mauritania
  • Niue
  • Rwanda
  • Saudi Arabia
  • Saint Kitts and Nevis
  • Solomon Islands
  • Tokelau
  • Tuvalu
  • Vanuatu
Moderate level of SARS-CoV-2 transmission
  • Fiji
  • Guinea
  • Kenya
  • Madagascar
  • Oman
  • Sao Tome and Principe
  • Uganda
  • Zimbabwe
High level of SARS-CoV-2 transmission
  • Anguilla
  • Armenia
  • Bahamas
  • Bangladesh
  • Belize
  • Bonaire
  • Bosnia-Herzegovina
  • Brazil
  • Bulgaria
  • Cambodia
  • Central African Republic
  • Cook Islands
  • Côte D'Ivoire
  • Cuba
  • Democratic Republic of Congo (Kinshasa)
  • Ecuador
  • Eswatini
  • Ethiopia
  • Gabon
  • Guatemala
  • India
  • Indonesia
  • Ireland
  • Kazakhstan
  • Kuwait
  • Liechtenstein
  • Malawi
  • Malaysia
  • Malta
  • Monaco
  • Montserrat
  • Netherlands
  • Northern Mariana Islands
  • Pakistan
  • Palau
  • Paraguay
  • Poland
  • Samoa
  • Saint-Barthélemy
  • Saint-Lucia
  • Seychelles
  • Sint Maarten
  • Slovakia
  • South Africa
  • Spain
  • Sweden
  • Timor-Leste
  • Togo
  • United Arab Emirates
Very high level of SARS-CoV-2 transmission
  • Afghanistan
  • Albania
  • American Samoa
  • Andorra
  • Aruba
  • Argentina
  • Australia
  • Austria
  • Azores
  • Bahrain
  • Barbados
  • Belgium
  • Bermuda
  • Bolivia
  • Brunei
  • Cayman Islands
  • Chile
  • Colombia
  • Costa Rica
  • Croatia
  • Cyprus
  • Czech Republic
  • Denmark
  • Dominican Republic
  • Estonia
  • Finland
  • France
  • French Guiana
  • French Polynesia
  • Georgia
  • Germany
  • Ghana
  • Greece
  • Grenada
  • Guadeloupe
  • Guam
  • Guyana
  • Honduras
  • Hong Kong
  • Hungary
  • Iceland
  • Israel
  • Italy
  • Jamaica
  • Japan
  • Kosovo
  • Latvia
  • Lebanon
  • Lithuania
  • Luxembourg
  • Marshall Islands
  • Martinique
  • Mauritius
  • Mexico
  • Micronesia (FSM)
  • Moldova
  • Mongolia
  • Montenegro
  • Mozambique
  • Nauru
  • Nepal
  • New Caledonia
  • New Zealand
  • North Macedonia
  • Panama
  • Peru
  • Philippines
  • Portugal
  • Puerto Rico
  • Qatar
  • Réunion
  • Romania
  • Russia
  • Saint Martin
  • Saint Vincent & the Grenadines
  • San Marino
  • Serbia
  • Singapore
  • Slovenia
  • Somalia
  • South Korea
  • Suriname
  • Switzerland
  • Taiwan
  • Tonga
  • Trinidad and Tobago
  • Tunisia
  • Türkiye
  • Turks and Caicos Islands
  • United Kingdom
  • United States
  • Virgin Islands (U.S.)
Unknown level of SARS-CoV-2 transmission
  • Algeria
  • Angola
  • Antigua and Barbuda
  • Azerbaijan
  • Belarus
  • Benin
  • Bhutan
  • Botswana
  • Burkina Faso
  • Burundi
  • Cameroon
  • Canary Islands
  • Chad
  • Comoros
  • Curacao
  • Djibouti
  • Dominica
  • Egypt
  • El Salvador
  • Gambia
  • Gibraltar
  • Greenland
  • Guinea-Bissau
  • Haiti
  • Iran
  • Iraq
  • Jordan
  • Kyrgyzstan
  • Laos
  • Lesotho
  • Liberia
  • Libya
  • Maldives
  • Mali
  • Mayotte
  • Morocco
  • Myanmar
  • Namibia
  • Nicaragua
  • Niger
  • Nigeria
  • North Korea
  • Norway
  • Papua New Guinea
  • Republic of Congo (Brazzaville)
  • Saint Pierre et Miquelon
  • Senegal
  • Sierra Leone
  • South Sudan
  • Sri Lanka
  • Sudan
  • Syria
  • Tajikistan
  • Tanzania
  • Thailand
  • Turkmenistan
  • Ukraine
  • Uruguay
  • Uzbekistan
  • Venezuela
  • Vietnam
  • Yemen
  • Zambia

References

Footnote 1

Committee to Advise on Tropical Medicine and Travel (CATMAT). Evidence Based Process for developing travel and tropical medicine related guidelines and recommendations. 2017; Available at: https://www.canada.ca/en/public-health/services/publications/diseases-conditions/evidence-based-process-developing-travel-tropical-medicine-guidelines-recommendations.html. Accessed July 5, 2021.

Return to footnote 1 referrer

Footnote 2

World Health Organization. WHO coronavirus (COVID-19) dashboard. 2021; Available at: https://covid19.who.int/. Accessed June 18, 2021.

Return to footnote 2 referrer

Footnote 3

Buitrago-Garcia D, Egli-Gany D, Counotte MJ, Hossmann S, Imeri H, Ipekci AM, Salanti G, Low N. Occurrence and transmission potential of asymptomatic and presymptomatic SARS-CoV-2 infections: A living systematic review and meta-analysis. PLoS medicine. 2020 Sep 22;17(9):e1003346.

Return to footnote 3 referrer

Footnote 4

Centers for Disease Control and Prevention. Post-COVID conditions: Overview. 2021; Available at: https://www.cdc.gov/coronavirus/2019-ncov/hcp/clinical-care/post-covid-conditions.html. Accessed July 7, 2021.

Return to footnote 4 referrer

Footnote 5

Nalbandian A, Sehgal K, Gupta A, Madhavan MV, McGroder C, Stevens JS, et al. Post-acute COVID-19 syndrome. Nat med. 2021 Mar 22;27(4):601-15.

Return to footnote 5 referrer

Footnote 6

Government of Canada. COVID-19 for health professionals: Transmission. 2021; Available at: https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/health-professionals/transmission.html. Accessed June 18, 2021.

Return to footnote 6 referrer

Footnote 7

World Health Organization. Transmission of SARS-CoV-2 - Implications for infection prevention precautions: Scientific brief. 2020; Available at: https://www.who.int/publications/i/item/modes-of-transmission-of-virus-causing-covid-19-implications-for-ipc-precaution-recommendations. Accessed July 7, 2021.

Return to footnote 7 referrer

Footnote 8

Government of Canada. COVID-19: Main modes of transmission. 2021; Available at: https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/health-professionals/main-modes-transmission.html. Accessed July 7, 2021.

Return to footnote 8 referrer

Footnote 9

O'Keeffe J, Freeman S, Nicol A. National Collaborating Centre for Environmental Health (NCCEH). The Basics of SARS-CoV-2 Transmission. Vancouver, BC: NCCEH. 2021 Mar.

Return to footnote 9 referrer

Footnote 10

Centers for Disease Control and Prevention. Scientific brief: SARS-CoV-2 transmission. 2021; Available at: https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/sars-cov-2-transmission.html. Accessed: July 15, 2021.

Return to footnote 10 referrer

Footnote 11

Centers for Disease Control and Prevention. Scientific brief: SARS-CoV-2 and surface (fomite) transmission for indoor community environments. 2021; Available at: https://www.cdc.gov/coronavirus/2019-ncov/more/science-and-research/surface-transmission.html. Accessed: July 15, 2021.

Return to footnote 11 referrer

Footnote 12

Committee to Advise on Tropical Medicine and Travel (CATMAT). Chapter 2 - Prevention and risk assessment: Canadian recommendations for the prevention and treatment of malaria. 2019; Available at: https://www.canada.ca/en/public-health/services/catmat/canadian-recommendations-prevention-treatment-malaria/chapter-2-prevention-risk-assessment.html. Accessed: July 5, 2021.

Return to footnote 12 referrer

Footnote 13

Boggild AK, Libman M, Greenaway C, McCarthy AE, on behalf of the Committee to Advise on Tropical Medicine and Travel (CATMAT). CATMAT statement on disseminated strongyloidiasis: Prevention, assessment and management guidelines. Can Comm Dis Rep 2016;42:12-19. doi: https://doi.org/10.14745/ccdr.v42i01a03.

Return to footnote 13 referrer

Footnote 14

Government of Canada. COVID-19: Improving indoor ventilation. 2021; Available at: https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/prevention-risks/covid-19-improving-indoor-ventilation.html. Accessed: July 10, 2021.

Return to footnote 14 referrer

Footnote 15

Centers for Disease Control and Prevention. Ventilation in Buildings. 2021; Available at: https://www.cdc.gov/coronavirus/2019-ncov/community/ventilation.html?s=09. Accessed July 10, 2021.

Return to footnote 15 referrer

Footnote 16

Rosca EC, Heneghan C, Spencer EA, Brassey J, Plüddemann A, Onakpoya IJ, Evans DH, Conly JM, Jefferson T. Transmission of SARS-CoV-2 associated with aircraft travel: a systematic review. Journal of travel medicine. 2021 Oct;28(7):taab133. doi: https://doi.org/10.1093/jtm/taab133

Return to footnote 16 referrer

Footnote 17

Willebrand KS, Pischel L, Malik AA, Jenness SM, Omer SB. A review of COVID-19 transmission dynamics and clinical outcomes on cruise ships worldwide, January to October 2020. Euro Surveill. 2022 Jan 6;27(1):2002113. doi: https://doi.org/10.2807/1560-7917.ES.2022.27.1.2002113

Return to footnote 17 referrer

Footnote 18

Saginur R, Birk H, on behalf of the Committee to Advise on Tropical Medicine and Travel (CATMAT). CATMAT statement on cruise ship travel. Can Comm Dis Rep 2005:31:ACS-8

Return to footnote 18 referrer

Footnote 19

Kordsmeyer AC, Mojtahedzadeh N, Heidrich J, Militzer K, von Münster T, Belz L, Jensen HJ, Bakir S, Henning E, Heuser J, Klein A. Systematic review on outbreaks of SARS-CoV-2 on cruise, navy and cargo ships. Int J Environ Res Public Health. 2021 Jan;18(10):5195. doi: https://doi.org/10.3390/ijerph18105195

Return to footnote 19 referrer

Footnote 20

US Department of Health and Human Services and Centers for Disease Control and Prevention. Temporary extension and modification of framework for conditional sailing order (CSO). 2021 Oct. Available at: https://www.cdc.gov/quarantine/cruise/covid19-cruiseships.html

Return to footnote 20 referrer

Footnote 21

O'Keeffe J, Eykelbosh A. National Collaborating Centre for Environmental Health (NCCEH). Understanding SARS-CoV-2 transmission in the ongoing COVID-19 pandemic. Vancouver, BC: NCCEH. 2021 Dec. Available at: https://ncceh.ca/documents/evidence-review/understanding-transmission-sars-cov-2-ongoing-covid-19-pandemic

Return to footnote 21 referrer

Footnote 22

Shen Y, Li C, Dong H, Wang Z, Martinez L, Sun Z, Handel A, Chen Z, Chen E, Ebell MH, Wang F. Community outbreak investigation of SARS-CoV-2 transmission among bus riders in eastern China. JAMA Intern Med. 2020 Dec 1;180(12):1665-71. doi:10.1001/jamainternmed.2020.5225

Return to footnote 22 referrer

Footnote 23

National Advisory Committee on Immunization. Canadian Immunization Guide. COVID-19 vaccine (chapter). Ottawa (ON): PHAC; 2022. Available at: https://www.canada.ca/en/public-health/services/publications/healthy-living/canadian-immunization-guide-part-4-active-vaccines/page-26-covid-19-vaccine.htm

Return to footnote 23 referrer

Footnote 24

National Advisory Committee on Immunization. Statements and publications: COVID-19. Available at: https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci.html#covid-19. Accessed September 10, 2021

Return to footnote 24 referrer

Footnote 25

Government of Canada. COVID-19: Recommendations for those vaccinated with vaccines not authorized by Health Canada for those staying in Canada to live, work or study. 2021; Available at: https://www.canada.ca/en/public-health/services/diseases/2019-novel-coronavirus-infection/guidance-documents/recommendations-those-vaccinated-with-vaccines-not-authorized-health-canada-staying-canada-live-work-study.html. Accessed: August 18, 2021

Return to footnote 25 referrer

Footnote 26

Regev-Yochay G, Amit S, Bergwerk M, et al. Decreased infectivity following BNT162b2 vaccination: a prospective cohort study in Israel. Lancet Reg Health Eur. 2021 Aug 1;7:100150-100150. doi: https://doi.org/10.1016/j.lanepe.2021.100150

Return to footnote 26 referrer

Footnote 27

Krutikov M, Palmer T, Tut G, Fuller C, Shrotri M, Williams H, et al. Incidence of SARSCoV-2 infection according to baseline antibody status in staff and residents of 100 long-term care facilities (VIVALDI): a prospective cohort study. Lancet Healthy Longev. 2021 Jun;2(6):e362,e370. doi: https://doi.org/10.1016/S2666-5247(21)00219-6

Return to footnote 27 referrer

Footnote 28

Townsend JP, Hassler HB, Wang Z, Miura S, Singh J, Kumar S, Ruddle NH, Galvani AP, Dornburg A. The durability of immunity against reinfection by SARS-CoV-2: a comparative evolutionary study. Lancet Microbe. 2021 Oct 1. doi: https://doi.org/10.1016/S2666-5247(21)00219-6

Return to footnote 28 referrer

Footnote 29

National Advisory Committee on Immunization. NACI rapid response: Updated guidance on COVID-19 vaccination timing for individuals previously infected with SARS-CoV-2. 2022; Available at: https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci/rapid-response-guidance-covid-19-vaccination-timing-individuals-previously-infected-sars-cov-2.html. Accessed March 28, 2022

Return to footnote 29 referrer

Footnote 30

Romero Starke K, Petereit-Haack G, Schubert M, Kämpf D, Schliebner A, Hegewald J, Seidler A. The Age-Related Risk of Severe Outcomes Due to COVID-19 Infection: A Rapid Review, Meta-Analysis, and Meta-Regression. Int J Environ Res Public Health. 2020 Aug 17;17(16):5974. doi: https://doi.org/10.3390/ijerph17165974

Return to footnote 30 referrer

Footnote 31

Gates M, Pillay J, Wingert A, Guitard S, Rahman S, Zakher B, et al. Risk factors associated with severe outcomes of COVID-19: An updated rapid review to inform national guidance on vaccine prioritization in Canada. medRxiv. 2021 May 22. doi: https://doi.org/10.1101/2021.04.23.21256014v2

Return to footnote 31 referrer

Footnote 32

Wingert A, Pillay J, Gates M, Guitard S, Rahman S, Beck A, et al. Risk factors for severe outcomes of COVID-19: a rapid review. medRxiv. 2020 Sep 1. doi: https://doi.org/10.1101/2020.08.27.20183434

Return to footnote 32 referrer

Footnote 33

Smith C, Odd D, Harwood R, Ward J, Linney M, Clark M, et al. Deaths in children and young people in England following SARS-CoV-2 infection during the first pandemic year: a national study using linked mandatory child death reporting data. medRxiv, 2021 July 7. doi: https://doi.org/10.1101/2021.07.07.21259779

Return to footnote 33 referrer

Footnote 34

Ward J, Harwood R, Smith C, Kenny SE, Clark M, Davis PJ, et al. Risk factors for intensive care admission and death amongst children and young people admitted to hospital with COVID-19 and PIMS-TS in England during the first pandemic year. medRxiv. 2021 Jan 1. doi: https://doi.org/10.1101/2021.07.01.21259785

Return to footnote 34 referrer

Footnote 35

Harwood R, Yan H, Da Camara NT, Smith C, Ward J, Tudur-Smith C, et al. Which children and young people are at higher risk of severe disease and death after SARS-CoV-2 infection: a systematic review and individual patient meta-analysis. medRxiv. 2021 Jan 1. doi: https://doi.org/10.1101/2021.06.30.21259763

Return to footnote 35 referrer

Footnote 36

Kompaniyets L, Agathis NT, Nelson JM, Preston LE, Ko JY, Belay B, et al. Underlying medical conditions associated with severe COVID-19 illness among children. JAMA network open. 2021 Jun 1;4(6):e2111182. doi: https://doi.org/10.1001/jamanetworkopen.2021.11182

Return to footnote 36 referrer

Footnote 37

Drouin O, Hepburn CM, Farrar DS, Baerg K, Chan K, Cyr C, Donner EJ, Embree JE, Farrell C, Forgie S, Giroux R et al. Characteristics of children admitted to hospital with acute SARS-CoV-2 infection in Canada in 2020. CMAJ. 2021 Sep 27;193(38):E1483-93. doi: https://doi.org/10.1503/cmaj.210053

Return to footnote 37 referrer

Footnote 38

National Advisory Committee on Immunization. Rapid response: Additional dose of COVID-19 vaccine in immunocompromised individuals following 1- or 2- dose series. 2021 Sept 10; Available at: https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci.html. Accessed: September 13, 2021

Return to footnote 38 referrer

Footnote 39

World Health Organization. Regulation and prequalification, emergency use listing: COVID-19 vaccines. 2021; Available at: https://www.who.int/teams/regulation-prequalification/eul/covid-19. Accessed September 10, 2021

Return to footnote 39 referrer

Footnote 40

Ong DS, Fragkou PC, Schweitzer VA, Chemaly RF, Moschopoulos CD, Skevaki C. How to interpret and use COVID-19 serology and immunology tests. Clinical Microbiology and Infection. 2021 May 8:27(7):981-986. doi: https://doi.org/10.1016/j.cmi.2021.05.001

Return to footnote 40 referrer

Report a problem or mistake on this page
Please select all that apply:

Thank you for your help!

You will not receive a reply. For enquiries, contact us.

Date modified: