Statement on COVID-19 and International Travel
Last content update: December 21, 2022
An Advisory Committee Statement (ACS)
Committee to Advise on Tropical Medicine and Travel (CATMAT)
Table of contents
- Key points/messages
- Assessing individual travel associated SARS-CoV-2 risk
- Host vulnerability assessment
- Other considerations
- Conflicts of interest
- Appendix: Types of activities and the relative likelihood of SARS-CoV-2 exposure
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.
- Travel advisors and their clients should verify any requirements (COVID-19 related or otherwise) in place at their destination(s) and for their return to Canada.
- CATMAT strongly recommends eligible travellers be adequately vaccinated with a Health Canada authorized COVID-19 vaccine before travel.
- The approach to vaccination, including the number and spacing of doses, and approaches for special populations, should be as recommended by the National Advisory Committee on Immunization (NACI). Current NACI recommendations on the use of COVID-19 vaccines can be found in the COVID-19 vaccine chapter of the Canadian Immunization Guide.
- Generally, CATMAT recommends against receiving the COVID-19 vaccine while in other countries.
- Infants who are not eligible for COVID-19 vaccines in Canada should not be vaccinated when travelling, even if the product is the same as those authorized for adolescent/adult use in Canada, or is authorized for use in children in other countries.
- In the absence of vaccination, or in the case that individuals have a diminished immune response to the vaccine, or are otherwise at an elevated risk for severe outcomes from infection, special attention should be paid to the use of individual public health measures for protection during travel.
- CATMAT suggests that, at the individual level, the main consideration when advising patients on travel in a COVID-19 environment should be the risk of severe COVID-19 associated outcomes. Accordingly, host vulnerability is the primary focus of the present guidance (see Table 2).
- Additional considerations include, the potential for transmission to others (particularly those who are higher risk for severe COVID-19), access to adequate medical services while abroad, potential for local healthcare facilities to be overwhelmed, and potential disruptions to travel as the COVID-19 situation evolves.
- The results of the host vulnerability assessment (ranging from low to very high) are explicitly linked to recommendations (see Table 2).
- For individuals considered at very high likelihood of developing severe COVID-19 if infected (Table 2), travelling with standby treatment of antiviral medication (e.g., nirmatrelvir/ritonavir) may be considered, particularly where access to good quality medical care and treatment is anticipated to be limited.
- CATMAT acknowledges that availability for this purpose may be limited, as eligibility criteria across most jurisdictions in Canada currently require a positive test result and mild/moderate symptoms.
- Pre-exposure prophylaxis for COVID-19 may be indicated in certain high-risk populations irrespective of travel plansFootnote 1. Travellers who are immune suppressed should discuss the use of monoclonal antibodies with their health care provider. If monoclonal antibodies are indicated and the traveller has access to treatment, they should initiate treatment prior to travel.
- Monoclonal antibodies have a continuously evolving role, and travellers should consult an expert to determine the most appropriate use of these agents for their individual situation and itinerary.
- Serologic testing for antibodies pre- or post-travel, as a surrogate for protection, is not recommended. There is no adequately validated correlation between serologic results from a given test and risk of severe outcomes.
This statement provides guidance for health care providers advising patients on health-related aspects of travel in a COVID-19-affected world. Policy and regulatory aspects of the COVID-19 response, such as requirements around vaccination and quarantine, are outside of the purview of this statement. For more information in this regard, 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.
This statement was developed by members of a CATMAT working group (WG), none of whom declared a relevant conflict of interest. This guideline was developed based on expert opinion informed by a narrative review of relevant evidence. The final statement and recommendations were approved by CATMAT.
Clinical and epidemiologic aspects of coronavirus disease 2019 (COVID-19) are well described elsewhere. The WHO COVID-19 Weekly Epidemiological Update, for example, provides up-to-date information on the global epidemiological situation as well as emerging knowledge related to SARS-CoV-2 variants of concern (VOCs) and variants of interest (VOIs).
Assessing individual travel associated SARS-CoV-2 risk
There are many factors that might affect the decision to travel during the ongoing SARS-CoV-2 pandemic. Some are structural, including travel and border regulations and requirements. This guideline does not consider these aspects, nor does it consider indirect but very important impacts of individual travel on others, for example the situation where a healthy traveller with mild illness may transmit SARS-CoV-2 to someone who is more vulnerable, or the potential for travel-associated spread of VOCs. Rather, the focus of this guidance is on:
- assessment of the traveller's (i.e. the host) vulnerability to severe COVID-19 related outcomes (Table 1); and,
- risk-management recommendations based on the host vulnerability assessment.
A key assumption within this guideline is that, in many circumstances and for a variety of reasons (including lack of travel health insurance coverage for COVID-19), travellers afflicted with COVID-19 will have reduced ability to access timely and/or sufficient health care support during their trip.
This guidance does not explicitly consider the reported level of SARS-CoV-2 transmission at a destination in our assessment. While there are important transmission heterogeneities between destinations, it is becoming increasingly difficult to accurately assess these due to differences in testing, surveillance, and reporting architectures. However, health care advisors should consult with Government of Canada Travel Advice and Advisories for destination-specific travel information and advice.
Finally, this guidance does not consider values and preferences of the traveller. Given that travellers will have divergent COVID-19 risk tolerances, it follows that their acceptance of travel recommendations will vary. It is in this context that travel-related decisions will be made, and where health care providers can help travellers make informed choices.
Host vulnerability assessment
The host vulnerability assessment estimates the qualitative likelihood that, if infected, a traveller will suffer significant acute harms, i.e. severe disease. The assessment framework was developed based on expert opinion, informed by a narrative review of relevant evidence. Age serves as the baseline for the host vulnerability assessment, given the well-established evidence of an increasing relative risk of severe COVID-19 outcomes with increasing age. Underlying medical conditions associated with an increased risk of severe outcomes from COVID-19 are based on evidence from systematic reviews or meta-analyses. Generally, CATMAT does not differentiate between conditions with respect to the resulting impact on the host vulnerability assessment.
The most important modifiable risk-management intervention for protection against severe COVID-19 is vaccination.
For most persons who have been adequately vaccinated (meaning, in accordance with NACI recommendations) and are expected to mount an appropriate response based on their known immune status, CATMAT suggests reducing the host vulnerability assessment by one level (shift to the left) from the baseline age-based estimate (see Table 1).
This approach means, for example, a person otherwise considered at high likelihood of significant SARS-CoV-2 infection-related harms based on the host vulnerability assessment, would be considered at moderate likelihood, if appropriately vaccinated as per NACI guidance.
Medical advisors should stay up-to-date with the latest guidance from NACI as vaccine recommendations may evolve over time.
COVID-19 related travel requirements and border measures
Recommendations applied in this guidance may differ from those applied to policy around travel requirements or border measures. Travellers should be advised to monitor both the requirements at their destination(s), and in Canada, including relevant provincial/territorial and local legislation, regulations, and policies, and that these could change during their travel period.
Age has the most profound population-level impact on the likelihood of severe COVID-19 and serves as a baseline for the host vulnerability assessment Footnote 2Footnote 3Footnote 4 (see Table 1). Importantly, age is confounded with other risk factors, particularly co-morbidities, such that the independent impact of age is reduced in adjusted analysesFootnote 2Footnote 3Footnote 4. Nonetheless, public health authorities use age as a fundamental baseline for assessing host vulnerability to, and consequent recommendations for the prevention of, COVID-19.
Host Vulnerability Assessment
|Age (in years) at start of travel||< 30||30 to 59||60 to 79||80+|
In general, if a traveller has been vaccinated in accordance with NACI recommendations, then the host vulnerability assessment can be reduced (shifted to the left) by one level, from the baseline age-based assessment.
Children under 6 months of age, for whom vaccines are not authorized
Very young, healthy children, for whom COVID-19 vaccines are not (at the time of writing) authorized are considered to be at very low risk for severe COVID-19 associated outcomes (barring any underlying medical conditions), even in the absence of vaccination Footnote 5Footnote 6Footnote 7Footnote 8.
Host vulnerability factors
The impact of other risk factors on the most serious COVID-19 outcomes is an area of ongoing investigation Footnote 9Footnote 10. A summary list of underlying medical conditions associated with more severe COVID-19 disease has been developed by the Public Health Agency of Canada (Box 1). In general, the risk of more severe disease increases with the number of medical conditions.
Box 1. Underlying medical conditions associated with increased risk for severe outcomes from COVID-19
Medical conditions (extracted from COVID-19 signs, symptoms, and severity of disease: A clinician guide from PHAC)Footnote aFootnote b
- Cerebrovascular disease
- Chronic kidney disease
- Chronic liver diseases (limited to: cirrhosis, non-alcoholic fatty liver disease, alcoholic liver disease, and autoimmune hepatitis)
- Chronic lung diseases (limited to: bronchiectasis, chronic obstructive pulmonary disease, interstitial lung disease, pulmonary hypertension, pulmonary embolism)
- Cystic fibrosis
- Diabetes mellitus (type 1 or type 2)
- Disabilities (e.g. Down syndrome, learning, intellectual, or developmental disabilities; ADHD; cerebral palsy; congenital disabilities; spinal cord injuries)
- Heart conditions (e.g. heart failure, coronary artery disease, cardiomyopathies, etc.)
- HIV infection
- Mental health disorders (limited to: mood disorders, including depression; schizophrenia spectrum disorders)
- Pregnancy and recent pregnancy
- Primary immunodeficiency diseases
- Smoking, current or former
- Solid organ or blood stem cell transplant
- Use of corticosteroids or other immunosuppressive medication
- Footnote a
For the most current list of conditions, health care advisors should refer to: COVID-19 signs, symptoms, and severity of disease: A clinician guide
- Footnote b
To aid in assessing immune suppression, 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.
Generally, CATMAT recommends increasing the host vulnerability assessment (shifting to the right) by at least one level if the traveller has any underlying medical condition in Box 1. The effect of vaccination (leftwards shift) and medical conditions (rightwards shift) are additive. It is recognized that this is a conservative approach, as some or all of the effect 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 two or more factors or particularly severe medical conditions, consider shifting the host vulnerability assessment to the right by two levels (indicating a larger increase in the risk of severe SARS-CoV-2 related harms). Box 2 provides examples of host vulnerability assessments.
Due to the relative paucity of evidence on the efficacy and effectiveness of vaccination in preventing severe outcomes from COVID-19 among populations with various known types of immune suppression, CATMAT recommends a conservative approach in applying the host vulnerability 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. Evidence continues to evolve on how to optimize protection in this diverse populationFootnote 11.
If the traveller has any of the immune suppressive 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 vulnerability 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 be subject to individual assessments and clinical discretion.
Immune suppressed travellers may be at risk both due to their underlying disease or due to the immunosuppressive medications they are taking and because their protection from vaccine may be reduced. Accordingly, providers may consider during an individual assessment whether the host vulnerability 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 treat these individuals in the host vulnerability assessment as not being adequately protected by vaccine, regardless of their actual vaccination status.
Box 2. Examples of host vulnerability assessments
Likelihood of severe outcomes decreased from the initial age-based host vulnerability assessment
A 70-year old individual who is healthy and without identified risk factors is planning to travel. The patient is adequately vaccinated, as per NACI recommendations.
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 vulnerability assessment by one level from their age-based risk (moving them from high to moderate).
Likelihood of severe outcomes increased from the initial age-based host vulnerability assessment
Scenario 1. A 40-year old person with Down syndrome is planning to travel. The patient also has diabetes, and is adequately vaccinated, as per NACI recommendations.
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 vulnerability assessment by two levels based on risk factors. However, as the individual is adequately protected by vaccine (which can reduce the vulnerability by one level), full adjustment will result in an increase of only one level, from moderate to high.
Scenario 2. A 50-year old individual with an allogeneic bone marrow transplant less than one year ago, and still receiving aggressive immune suppressive medication, is planning to travel. They are adequately vaccinated, as per NACI recommendations
This patient starts at moderate risk due to age. However, there is reason to assume that the individual is both at risk of severe disease due to major immune suppression, and lower immunogenicity of vaccination. Consider increasing the host vulnerability assessment by two levels due to the severity of the immune suppression, to very high and do not change the assessment based on vaccination status.
Among children, risk factors for severe disease include underlying medical conditions such as type 1 diabetes, neurological conditions, chronic pulmonary diseases (other than mild, controlled asthma), cardiac and circulatory congenital anomalies, obesity, and immune dysregulation associated with Down Syndrome and other immune compromising conditionsFootnote 8Footnote 12; many of which are the same as have been identified in adults (see Box 1)Footnote 2Footnote 3Footnote 4. Hence, CATMAT recommends that the same approach (to increase the host vulnerability assessment level from the initial age-based assessment based on presence of other risk factors) be applied when assessing children. Some preventive therapies, such as antivirals or monoclonal antibodies, may not be indicated for use in children depending on age and weight requirements for eligibility. Expert opinion should be sought in guiding preventive pharmacologic options in vulnerable children.
Access to adequate medical care
Travellers, particularly those individuals deemed to be at moderate-to-very 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. In many circumstances, access to high quality specialized care will be more difficult to obtain. Further, any travel and treatment costs incurred as a result of COVID-19 might not be covered by medical travel insurance.
Travel itinerary and activities
The types of activities and actions that individuals undertake will 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 (i.e. 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) filter Footnote 13Footnote 14.
For individuals who are considered to have high or very high host vulnerability, it is recommended that activities associated with an increased exposure likelihood be minimized (see Appendix).
Vaccination outside of Canada
In general, CATMAT advises against receipt of vaccines not authorized in Canada, and/or offered in international locations. In some countries, it may be difficult to verify that vaccines are manufactured, stored, and administered under optimal conditions. Rather, emphasis should be placed on receiving vaccinations before leaving Canada.
In some circumstances, e.g., for long-term travellers and expatriates, vaccination outside of Canada might be unavoidable. If this is the case, then the traveller 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 15.
Serologic testing for antibodies pre- or post-travel, as a surrogate for protection, is not recommended. Although commercial tests are available, they are of highly variable quality and accuracy. There is no adequately validated correlation between serologic results from a given test and risk of severe outcome.
The final host vulnerability assessment is comprised of the baseline assessment (based on the traveller's age, see Table 1), and any subsequent adjustments based on vaccination status (as per NACI guidance) and underlying medical conditions. Recommendations based on a traveller's final assessment are provided in Table 2. Additional considerations for very high risk travellers, specifically, are discussed below Table 2. The following broad guidance also applies to all individuals intending to travel outside of Canada:
- Eligible individuals should be adequately vaccinated against COVID-19, as per NACI guidance, while in Canada.
- Travellers should verify any travel requirements in place at their destination(s) and in Canada.
- Travellers should be familiar with Canadian recommendations for self-protection and be equipped to implement multiple individual public health measures based on their own preferences and any requirements at their destination.
|Host vulnerability assessment||Recommendations|
|Low||Comply with all local COVID-19 regulations, practice proper respiratory etiquette and hand hygiene, and stay home if you are sick.|
|Moderate||Recommendations as per low risk, and consider additional non-medical individual public health measures (such as mask wearing in crowded/indoor settings, physical distancing), if not already specified by local regulations at the destination(s).|
|High||Recommendations as per low and moderate risk and consider limiting exposure length to as short as reasonably possible / choosing alternate activities when possible (see Appendix).|
|Very high||Recommendations as per low to high risk levels and consider deferring travel plans altogether. For certain travellers, if there is the possibility of reducing risk (e.g. reducing immune suppression, or treatment/management of a high-risk condition over time) then travellers should consider postponing travel.
Health care providers should consider advising intermittent testing during travel, even in the absence of symptoms or known contacts. Additional considerations for very high risk travellers are provided below.
Additional considerations for very high risk travellers
For individuals at very high risk for severe COVID-19, the following additional therapies may be considered, based on shared clinical decision making:
- Use of standby treatment with antiviral medication (eg: nirmatrelvir/ritonavir) in the absence of any drug-drug interactions, particularly where access to medical care and treatment may be limited, should the traveller become ill.
- CATMAT acknowledges that the availability of antiviral medication for this purpose may be limited at this time, as eligibility criteria across most jurisdictions require a positive test result and mild/moderate symptoms.
- Pre-exposure prophylaxis for COVID-19 may be indicated in certain high-risk populations, irrespective of travel plans. Providers should discuss whether the patient's medical conditions might warrant mitigation of infection using pre-exposure monoclonal antibodies. If monoclonal antibodies are indicated and the traveller has access to treatment, they should initiate treatment prior to travel.
- Regarding monoclonal antibodies, any provincial or territorial recommendations for use of monoclonal antibodies may also apply to travellers.
- monoclonal antibodies have a continuously evolving role, and travellers should consult an expert to determine the most appropriate use of these agents for their individual situation and itinerary.
This statement was prepared by the COVID-19 Working Group: Libman M (Chair), Bui Y, Lagacé-Wiens P, Rossi C, Schofield S, Vaughan S, 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 thank Andrea Boggild (member emeritus) for her contribution to earlier versions of the statement. CATMAT also acknowledges 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), Acharya A, Bogoch I, Bui Y, Greenaway C, Lagacé-Wiens P, Lee J, Plewes K, Vaughan S,.
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), Rossi C (Medical Intelligence, Department of National Defence), Schofield S (Pest Management Entomology, Department of National Defence), and Zimmer R (Biologics and Radiopharmaceutical Drugs Directorate, Health Canada).
Conflicts of interest
Appendix: Types of activities and the relative likelihood of SARS-CoV-2 exposure
The appendix below provides a non-exhaustive list of activities characterized by their anticipated SARS-CoV-2 exposure level. For those individuals who are considered at high or very high risk based on the host vulnerability assessment, one way to mitigate risk would be to modify activities to limit or reduce the risk of exposure.
Types of activities that are considered to be at relatively lower or higher likelihood of exposure to SARS-CoV-2
Lower density outdoor environment. Distancing possible.
Examples: Trekking in a wilderness area, playing golf, individual exercise outdoors, walking in uncrowded areas.
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.
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).
- Footnote 1
Canadian Public Health Association. Long acting monoclonal antibodies: Information for Canadians on COVID-19 pre-exposure prophylaxis (prevention) with monoclonal antibodies. 2022; Available at: https://www.cpha.ca/laab. Accessed August 18, 2022.
- Footnote 2
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
- Footnote 3
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.
- Footnote 4
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.
- Footnote 5
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
- Footnote 6
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
- Footnote 7
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
- Footnote 8
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
- Footnote 9
Kompaniyets L, Pennington AF, Goodman AB, Rosenblum HG, Belay B, Ko JY, et al. Underlying medical conditions and severe illness among 540,667 adults hospitalized with COVID-19, March 2020–March 2021. Prev Chronic Dis 2021;18:210123. DOI: http://dx.doi.org/10.5888/pcd18.210123
- Footnote 10
Centers for Disease Control and Prevention. Scientific brief: Evidence used to update the list of underlying medical conditions associated with higher risk for severe COVID-19. 2022; Available at: https://www.cdc.gov/coronavirus/2019-ncov/science/science-briefs/underlying-evidence-table.html. Accessed: July 07, 2022.
- Footnote 11
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.html
- Footnote 12
Choi JH, Choi SH, Yun KW. Risk ractors for severe COVID-19 in children: A systematic review and meta-analysis. J Korean Med Sci. 2022 Feb 7;37(5):e35. doi: 10.3346/jkms.2022.37.e35
- Footnote 13
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 07, 2022.
- Footnote 14
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.
- Footnote 15
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 July 07, 2022.
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