Archived 20: NACI rapid response: Booster dose in long-term care residents and seniors living in other congregate settings [2021-09-28]
Publication date: September 28, 2021
Notice to reader
This is an archived version. Please refer to current COVID-19 vaccine pages:
On this page
- Summary of evidence
- Research priorities
- Appendix A
The National Advisory Committee on Immunization (NACI) is an External Advisory Body that provides the Public Health Agency of Canada (PHAC) with independent, ongoing and timely medical, scientific, and public health advice in response to questions from PHAC relating to immunization.
In addition to burden of disease and vaccine characteristics, PHAC has expanded the mandate of NACI to include the systematic consideration of programmatic factors in developing evidence-based recommendations to facilitate timely decision-making for publicly funded vaccine programs at provincial and territorial levels.
The additional factors to be systematically considered by NACI include: economics, ethics, equity, feasibility, and acceptability. Not all NACI Statements will require in-depth analyses of all programmatic factors. While systematic consideration of programmatic factors will be conducted using evidence-informed tools to identify distinct issues that could impact decision-making for recommendation development, only distinct issues identified as being specific to the vaccine or vaccine-preventable disease will be included.
This statement contains NACI’s independent advice and recommendations, which are based upon the best current available scientific knowledge. This document is being disseminated for information purposes. People administering the vaccine should also be aware of the contents of the relevant product monograph. Recommendations for use and other information set out herein may differ from that set out in the product monographs of the Canadian manufacturers of the vaccines. Manufacturer(s) have sought approval of the vaccines and provided evidence as to its safety and efficacy only when it is used in accordance with the product monographs. NACI members and liaison members conduct themselves within the context of PHAC’s Policy on Conflict of Interest, including yearly declaration of potential conflict of interest.
Canadians residing in long-term care (LTC) homes and seniors living in other congregate settings, such as retirement homes or assisted-living facilities, are at increased risk for COVID-19 infection because of their daily interactions with other residents and staff. They are also at increased risk for severe disease because of their age and underlying medical conditions. While only representing approximately 1.1% of the Canadian population, LTC residents accounted for approximately two thirds of all reported deaths associated with COVID-19 during the first and second waves of the pandemic, and half of all reported deaths to dateFootnote 2.
Older adults and LTC residents in particular may respond less well to vaccination and have a less durable response to vaccines and/or past infection compared to younger adults due to immunosenescence associated with ageing and/or underlying immunocompromising conditions or medications. Older Canadians residing in congregate living settings were prioritized for the COVID-19 vaccine when the vaccines were first authorized; therefore, many completed their COVID-19 vaccination series early in the vaccine roll-out, leaving more time for waning should it occur. As well, many received their vaccines using the manufacturers’ recommended interval of 21 days for Pfizer-BioNTech Comirnaty and 28 days for Moderna Spikevax. Evidence to date suggests that, compared to longer intervals, shorter intervals between the first and second doses result in lower immune responses and therefore may also result in more rapid waning of protection, including against variants of concern (VOC).
There is currently a resurgence of COVID-19 cases in regions of Canada fuelled by the highly transmissible B.1.617.2 (Delta) variant. On September 10, 2021, B.1.617.2 (Delta) accounted for 75% of all newly reported cases and 90% of newly reported VOC casesFootnote 3. Infections in fully vaccinated people have occurred with the B.1.617.2 (Delta) variant. These infections can be due to a combination of evasion of vaccine-induced immunity mounted against the original (wild-type) SARS-CoV-2 strain, waning of immunity and protection over time (i.e., secondary vaccine failure), and/or inadequate response to the primary vaccination series (i.e., primary vaccine failure). Like with other VOC, vaccinated individuals infected with B.1.617.2 (Delta) are less likely to develop severe disease; however, vaccinated individuals infected with B.1.617.2 (Delta) may be more infectious to others compared to those infected with other strains, potentially facilitating transmission in congregate living settingsFootnote 4.
The intent of a booster dose is to restore protection that may have waned over time in individuals who responded adequately to a primary vaccine series. This is distinguished from the intent of an additional dose beyond the standard primary vaccine series, such as that discussed in the recent rapid response statement on immunocompromised individualsFootnote 5, which is to provide an opportunity for individuals who may not have achieved an adequate level of protection from the standard primary vaccine series to mount a better immune response.
Offering a booster dose of COVID-19 vaccine to LTC residents and seniors living in other congregate settings is a strategy to enhance protection and prevent outbreaks among this vulnerable population. A booster dose will provide an opportunity raise antibody titres which are likely to result in better protection, and longer duration of protection, including against SARS-CoV-2 VOCFootnote 6. There is also a small proportion of older adults residing in congregate living settings who have failed to respond to the primary series. Some of these individuals may be eligible for an additional dose as part of the recommendations for immunocompromised individuals, however those who are not will be better protected by a booster dose offered to the broader cohort.
Several countries have recently begun offering or plan to offer additional/booster doses to their general population, residents of LTC homes and/or older adults. Experiences in other countries may not necessarily be generalizable to Canada as a number of factors may differ between countries including: the vaccine product(s) used to complete the primary series; time since last dose; the intervals between first and second doses; indirect protection from higher vaccination coverage; and the use of other public health measures, such as masking and physical distancing policies.
The objective of this guidance document is to provide advice on the use of a booster dose of a COVID-19 vaccine following receipt of a primary series for LTC residents and seniors living in other congregate settings in Canada.
NACI has reviewed available direct and indirect evidence on COVID-19 vaccine effectiveness (VE), waning antibody responses, and current COVID-19 outbreak epidemiology on September 7, 2021, and September 14, 2021. Additional details on the rapid review conducted to assess VE following a primary COVID-19 vaccine series in LTC residents and seniors living in other congregate settings is available in Appendix A. NACI also received an ethics analysis from the PHAC Public Health Ethics Consultative Group (PHECG) evaluating ethical considerations of recommending an off-label booster dose of a COVID-19 vaccine to LTC residents and seniors living in other congregate settings, prepared on September 3, 2021. Much of the ethics analysis is reproduced or adapted within this NACI statement, with permission from PHECG.
Following a comprehensive review of available evidence, NACI approved the recommendations outlined below on September 28, 2021. Details of NACI’s evidence-informed recommendation development process can be found elsewhere.
Summary of evidence
Burden of illness
Throughout the pandemic, LTC residents and seniors living in other congregate settings have faced a disproportionate burden of COVID-19-associated harmsFootnote 9. Residents living in these settings are at higher risk of sustained transmission and outbreaks due to the congregate living environment and are at high risk for severe outcomes of COVID-19 due to older age and a high prevalence of medical comorbiditiesFootnote 10. While over 50% of deaths in Canada to date are from LTC residents, this population only constituted approximately 3.6% of the confirmed cases nationally, with a cumulative case fatality rate estimated at 27%Footnote 11. This population was also impacted by indirect consequences of COVID-19. Some settings where residents regularly received care from family members or other caregivers were significantly impacted when restrictions on essential visitors were imposed. Residents experienced an overall decline in care where there were shortages in staffing, caused by factors such as pre-existing infrastructure and operational planning, and outbreaks which resulted in absenteeism due to illness amongst staffFootnote 2. There were also decreases in physician visits and decreased transfers to hospital for non-COVID-19-related reasons, adding to the increased risks faced by this populationFootnote 2.
Residents of congregate living settings that provide care for seniors were prioritized for COVID-19 vaccination during the initial roll-out of vaccines in December 2020Footnote 12, and have one of the highest vaccination coverage in Canada. By April 10, 2021 approximately 96.7% of LTC residents had received at least one dose of COVID-19 vaccine, although vaccine uptake amongst LTC staff has been more variableFootnote 13. Most LTC residents received an mRNA COVID-19 vaccine (Pfizer-BioNTech Comirnaty or Moderna Spikevax) at the manufacturer-specified interval between dose 1 and dose 2 (21 to 28 days, respectively). However, there were differences in COVID-19 vaccination programs across Canada and some seniors in congregate living settings received an extended interval based on jurisdictional roll-out strategies.
Recent epidemiological trends
LTC homes have recently experienced an increase in the incidence of COVID-19 outbreaks in some Canadian jurisdictionsFootnote 14, likely fueled by the highly transmissible B.1.617.2 (Delta) variant. Since early August, the weekly number of outbreaks in LTC homes has trended upward to levels last observed towards the end of the third wave, in May 2021 (data cut off September 11, 2021)Footnote 14.
Recent data from the National Institute on Ageing (NIA), which tracks outbreaks, infections and deaths amongst residents and workers at LTC homes in Canada, has also demonstrated that confirmed SARS-CoV-2 infections and deaths from COVID-19 have rapidly increased amongst LTC residents since mid-AugustFootnote 15. For the period of August 23 to September 7, 2021, 501 cases and 62 COVID-19 associated deaths in LTC residents across Canada were recorded, indicating a recent trend in rising cases and deathsFootnote 15, which may be driven by some jurisdictions with elevated rates of community transmission. Although a vast majority of the LTC population is fully vaccinated (>92%), it is currently unclear the extent to which these trends are being driven by unvaccinated individuals in direct contact with LTC residents. Increasing vaccine coverage among healthcare workers, volunteers, visitors and other members of the community remains a critical intervention and high priority for protecting those living in LTC and congregate living settings.
mRNA COVID-19 vaccine effectiveness and immunogenicity over time
Vaccine effectiveness over time in adult populations
Several emerging studies conducted when B.1.617.2 (Delta) was the main circulating VOC report a decline in vaccine effectiveness (VE) against infection for mRNA COVID-19 vaccines that correlate with time since second dose. Effectiveness estimates against infection were high one to three months following second dose; however, the estimates trended downwards after 15 weeks following second dose (ranging from 29.7% (95% CI: 21.7 to 36.9%)Footnote 16 to 53% (95% CI: 39% to 65%)Footnote 17. However, high VE against severe disease (i.e., hospitalization or death) remained stable for the maximum study follow-up up of 6 monthsFootnote 16 following second dose, and studies are ongoing.
A nation-wide study from Israel on VE of Pfizer-BioNTech Comirnaty based on time since second dose recently reported that VE against infection (from July 11 to 31, 2021 when B.1.617.2 (Delta) predominated) declined, and rate of infection increased, correlating with increasing time since vaccination in younger individuals (16 to 39 years of age), adults 40 to 59 years of age, and older adults (60 years of age and older). At the time of this study, older adults vaccinated with Pfizer-BioNTech Comirnaty in January 2021 had a VE of 57% (95% CI: 52% to 62%) compared to a VE of 75% for those vaccinated more recently in May 2021 (95% CI: 58% to 85%). VE against severe disease declined slightly but remained high for individuals 60 years of age and older that received their last dose in January (VE 86%; 95% CI: 82% to 90%) compared to March 2021 (VE 91%; 95% CI: 85% to 95%)Footnote 18. Caution should be taken on interpretation of these studies as they have not yet been peer-reviewed. In addition, observational studies need to be interpreted with caution acknowledging potential bias or confounding.
Vaccine effectiveness over time in LTC residents and seniors living in other congregate settings
Little evidence is available to directly inform rates of waning vaccine protection in LTC residents and older adults in other congregate living settings.
A rapid literature review of studies reporting VE following a primary COVID-19 vaccine series in LTC residents and older adults in congregate living settings identified 11 observational studies from six different countries (Spain n=3Footnote 19Footnote 20Footnote 21; France n=2Footnote 22Footnote 23; Denmark n=2Footnote 24Footnote 25; Norway n=1Footnote 26; USA n=2Footnote 27Footnote 28; Canada n=1Footnote 29) and included over 750,000 residents (See Appendix A).
VE estimates on COVID-19-related hospitalization and/or death in LTC residents reported similar estimates (75% [95% CI: 46% to 89%] to 97% [95% CI: 95% to 98%]) across varying study dates (follow-up ended between March and June 2021). One longitudinal US-based study provided evidence of waning protection against infection in LTC residents and older adults in congregate living settings. This study demonstrated a significant decline in VE against SARS-CoV-2 infection over time (from 74.7% [95% CI: 70.0% to 78.8%] in March – May 2021 to 53.1% [95% CI: 49.1% to 56.7%] in June 21 – August 1), which authors suggest may be in part due to the increasing prevalence of the B.1.617.2 (Delta) variantFootnote 28. There was no difference in VE between Pfizer-BioNTech Comirnaty and Moderna Spikevax mRNA vaccines. Duration of follow-up of other included studies was insufficient to provide evidence on waning of VE in this population.
Immunogenicity over time in LTC residents and seniors living in other congregate settings
No immunological correlate of protection has been determined for SARS-CoV-2 infection or COVID-19 disease; therefore, all immunological evidence in support of vaccine efficacy is indirect and cannot directly be used to estimate efficacy. Nonetheless, a growing body of evidence supports an association between anti-SARS-CoV-2 neutralizing antibodies and protection against infection and severe disease. Some of this evidence can be used to complement or anticipate trends in protection that might emerge for vulnerable populations.
Several Canadian-led serology studies in LTC residents report that two doses of Moderna Spikevax or Pfizer-BioNTech Comirnaty elicit a strong initial antibody response capable of neutralizing SARS-CoV-2Footnote 30Footnote 31. In preprints, which are not peer reviewed, humoral immune responses in LTC residents waned significantly after three monthsFootnote 32, and in one study approximately 20% of residents failed to demonstrate a detectable neutralizing antibody response to the wild-type or B.1.351 (Beta) variant three to five months following second dose of mRNA COVID-19 vaccineFootnote 30. Emerging data from an ongoing longitudinal serology study in LTC residents and staff in Ontario found the majority of LTC residents failed to demonstrate a detectable neutralization titer against the B.1.617.2 (Delta) strain at six months after completing the vaccine series (A McGeer, personal communication). Earlier time points two to four weeks following second dose in the same study reported lower antibody responses in LTC residents compared to LTC staff (serving as younger age group comparator) across a panel of wild-type virus and VOC (Alpha, Beta, and Gamma)Footnote 31. Moreover, antibody levels tended to be higher for LTC residents vaccinated with Moderna Spikevax than Pfizer-BioNTech ComirnatyFootnote 30Footnote 31; however, neither study reported an assessment of the correlation of product-specific immunogenicity differences with vaccine effectiveness.
Summary of evidence on booster doses of mRNA COVID-19 vaccines in LTC residents and seniors living in other congregate settings
Current studies of booster doses of mRNA COVID-19 vaccines
There are currently no data available on the use of booster doses in LTC residents or seniors living in other congregate settings. Both mRNA vaccine manufacturers (Moderna and Pfizer-BioNTech) are concluding randomized controlled trials on booster doses (with formulations using the wild-type and/or variant strains) evaluating their reactogenicity and immunogenicity. While data are currently limited for older adults, early results show a favourable reactogenicity profile and evidence of boosted immune responses in the overall study populations. It should be noted that Moderna Spikevax is being studied at a dose lower than the current 100 mcg formulation in some booster trials which may confer reduced reactogenicity.
Recent studies from Israel have demonstrated short-term effectiveness of a third dose of Pfizer-BioNTech Comirnaty compared to VE in cohorts who received two doses, in those 60 years of age and older as well as those 40 years of age and older. Bar-On et al. reported >10-fold reduction of confirmed infection and severe illness among individuals ≥ 60 years of age at 12 days or more (up to 41 days) following receipt of a third doseFootnote 7. Similarly, a retrospective study (not yet peer reviewed) showed individuals ≥ 40 years of age had a 70% to 84% reduction in the odds of testing positive for SARS-CoV-2 infection 14-20 days after receiving a COVID-19 boosterFootnote 8.
In data available to date, there have been no notable differences in the frequency or duration of local and systemic adverse events following a booster dose compared to those reported following Dose 2 in participants 16-55 years of age. It is unknown whether there is an increased risk of adverse reactions, such as myocarditis/pericarditis following a third dose. However, myocarditis/pericarditis would be less of a concern for older adults in congregate living settings as this adverse event occurs most frequently in adolescents and younger adults under 30 years of age.
NACI continues to review emerging evidence on booster doses as the vaccines are considered by regulators around the world, and will issue further advice as needed. Notably, the United Kingdom (UK) regulatory authority (Medicines and Healthcare products Regulatory Authority [MHRA]) recently authorised booster doses for Pfizer-BioNTech Comirnaty, and the UK Joint Committee on Vaccination and Immunisation (JCVI) has recommended that mRNA booster doses be provided to priority groupsFootnote 33.
For further information, please refer to NACI's Recommendations on the use of COVID-19 vaccines.
Ethics and equity considerations
The objective of NACI’s guidance in this pandemic has been to provide evidence-informed recommendations on the effective, ethical, and equitable use of COVID-19 vaccines authorized and available for use in CanadaFootnote 12Footnote 34. The foundational elements that have guided ethical decision-making for these recommendations are consistent with those outlined in NACI’s Ethics, Equity, Feasibility and Acceptability (EEFA) FrameworkFootnote 35. When initial supplies of authorized COVID-19 vaccines became available to Canadians, NACI prioritized residents of congregate living settings that provide care for seniors to receive initial doses. This prioritization was based on a comprehensive analysis using the EEFA framework as well as evidence available on a population-based risk-benefit analysis (taking into consideration risk of exposure and severe illness and death from COVID-19), COVID-19 epidemiology, and vaccine characteristics (e.g., safety and efficacy)Footnote 12Footnote 36Footnote 37Footnote 38Footnote 39. NACI also considered these factors when making the current recommendation for a booster dose of COVID-19 vaccine in LTC residents and seniors living in other congregate settings.
NACI developed guidance on the prioritization of initial doses of COVID-19 vaccines in the context of limited initial vaccine supply, focusing on key populations with increased risk of exposure to SARS-CoV-2 infection and/or at increased risk of severe COVID-19 disease. Waning of protection is expected to be observed in these populations first, as they completed their vaccinations early and often with a shorter interval between doses.
Besides a general duty to protect the public’s health, Canada also has a duty to protect the most vulnerable. The precautionary principle supports offering a booster dose of a COVID-19 vaccine to those who are at greatest risk of serious or irremediable harms due to COVID-19, prior to a significant degree of waning VE against severe outcomes being observed. LTC residents and seniors living in other congregate settings have been distinctly more vulnerable than other populations, and have faced disproportionate harms from the COVID-19 pandemic, often as a result of a direct failure to act to protect this specific population in earlier stages of the pandemic. Accordingly, compensatory justice implies that Canada has a special responsibility to protect LTC residents against COVID-19 going forward.
Unvaccinated individuals are at the highest risk for SARS-CoV-2 infection, and this may include a number of residents of congregate living settings due to the dynamic nature of this group (average length of stay is approximately 18 months)Footnote 40. While there is a role for booster doses in protecting this group, ensuring completion of a primary series of an authorized COVID-19 vaccine for unvaccinated residents, healthcare workers, volunteers and close contacts will continue to offer the most benefit. Staff members and visitors can introduce the SARS-CoV-2 virus from the community into the congregate living setting resulting in infection and outbreaks among residents, therefore very high primary-series coverage for these individuals is also of paramount importance.
Although not within the purview of NACI’s specific mandate, NACI acknowledges the importance of global equity in relation to the COVID-19 pandemic. It is impossible to separate decision-making about COVID-19 vaccine booster doses in Canada from the issue of global vaccine equity and the global context of the pandemic. The benefits of offering booster doses domestically must be carefully considered against the demonstrable need for a primary series of COVID-19 vaccine abroad. In addition to promoting equity, supporting public health globally also benefits the populations of high-income countries by reducing the global spread of COVID-19 and potentially the emergence of VOC.
Interval between the primary series and a booster dose
There is evidence that longer intervals between doses in the primary series of COVID-19 vaccines result in higher antibody responses and also higher efficacy/effectivenessFootnote 41Footnote 42Footnote 43Footnote 44. However, there are currently limited data to determine the optimal interval between the completion of the primary series and administration of a booster dose. Immunogenicity data collected at 6 months following the primary series in LTC residents indicate waning immunity in this population. Studies currently investigating booster doses are using intervals as little as 3 monthsFootnote 45Footnote 46 from the completion of the primary series, with most using 6 months or more. Submissions filed with regulatory authorities in the US, EU and Canada are for 6 months or more following the second dose, which aligns with the interval being used in booster dose clinical trials for Pfizer-BioNTech Comirnaty and Moderna Spikevax.
A longer interval between the primary series and a booster dose is likely to result in a better immune response. However, delaying the booster dose will increase the period during which individuals who may have reduced protection against SARS-CoV-2 infection are vulnerable to infection, although protection against severe outcomes will likely be more durable after the primary series. Practically, some residents may receive shorter intervals due to operational considerations when boosting entire facilities.
Vaccine product considerations
Studies reporting antibody levels over time in LTC residents who received a primary series with Moderna Spikevax showed a higher response than those who received a primary series with Pfizer-BioNTech Comirnaty. This was also observed in a recent NACI review on immunocompromised individuals. However, vaccine effectiveness against preventing severe outcomes, such as hospitalizations and deaths has been comparable between the vaccines. Some studies have noted somewhat higher effectiveness of Moderna Spikevax than Pfizer-BioNTech Comirnaty against the B.1.617.2 (Delta) variantFootnote 47Footnote 48Footnote 49, although there may be differences in timing of use and populations who received each product that could contribute to these differences. The one study conducted in LTC residents did not find a difference in vaccine effectiveness between productsFootnote 28. While some evidence is available on viral vector booster doses, the data have not yet been reviewed by NACI.
It is important to acknowledge that the regulatory submission for a Moderna booster dose is likely to be for half the current dosage of Moderna Spikevax (i.e., a 50 mcg booster dose vs. 100 mcg full dose). However, as older adults have dampened immune function, and may need to receive a higher dose formulation of a vaccine or an immunostimulatory adjuvant to increase the potency of their response to vaccines, this population may benefit from a full dose (100 mcg) of Moderna Spikevax as a booster dose.
For further information on the NACI review on immunocompromised individuals, please refer to NACI’s rapid response on Additional dose of COVID-19 vaccine in immunocompromised individuals following 1- or 2- dose primary series.
For a primary series, NACI continues to recommend the following for all individuals in the authorized age group, including LTC residents and seniors living in other congregate settings:
- NACI preferentially recommends that a complete series with an mRNA COVID-19 vaccine should be offered to individuals in the authorized age group without contraindications to the vaccine. (Strong NACI Recommendation)
- NACI recommends that a viral vector COVID-19 vaccine may be offered to individuals in the authorized age group without contraindications to the vaccine to initiate a series when other authorized COVID-19 vaccines are contraindicated or inaccessible. Informed consent should include discussion about the risk and symptoms of VITT, as well as the need to seek immediate medical care should symptoms develop. (Discretionary NACI Recommendation)
Based on ethical considerations, recent trends in COVID-19 epidemiology, and accumulating evidence on waning of COVID-19 vaccine immunogenicity and effectiveness over time, NACI now recommends the following in addition to the above:
- For all long-term care residents and seniors living in other congregate settings who have received a primary COVID-19 vaccine series (with a homologous or heterologous schedule using mRNA or viral vector vaccines) NACI recommends that a booster dose of an authorized mRNA COVID-19 vaccine should be offered. This dose should be offered at a recommended interval of at least 6 months after the primary series has been completed. Informed consent for a booster dose should include discussion about what is known and unknown about the risks and benefits, including the off-label status of NACI's recommendation. (Strong NACI Recommendation)
- 3a. A booster dose of an authorized viral vector vaccine should only be considered when other authorized COVID-19 vaccines are contraindicated or inaccessible. Informed consent should include discussion about the risk and symptoms of VITT, as well as the need to seek immediate medical care should symptoms develop. (Discretionary NACI Recommendation)
Additional considerations, summary of evidence and rationale
- Based on the ethics principles of precaution and compensatory justice, NACI has determined that there is an immediate need to provide recommendations on a booster dose of COVID-19 vaccine to all LTC residents and seniors living in other congregate settings, where signs are emerging that protection might not be expected to persist as long as other populations in Canada.
- The combined factors of high risk of exposure, high risk of severe outcomes, time since last dose, and interval between doses in the primary series, and older age/immunosenescence create conditions that could particularly exacerbate waning vaccine protection against severe outcomes in this vulnerable population.
- Informed consent for a booster dose should include discussion about what is known and unknown about the risks and benefits, including the off-label status of NACI's recommendation.
- There are limited data showing waning vaccine effectiveness in LTC residents and seniors living in other congregate settings. However, there is a larger body of evidence where waning vaccine effectiveness against infection is being observed in countries that followed the manufacturer-recommended intervals for mRNA vaccines. Protection against severe outcomes remains high.
- Evidence from Canadian studies suggests that although two doses of mRNA vaccine elicit a strong initial antibody response in most LTC residents which is capable of neutralizing SARS-CoV-2, a majority of these individuals fail to demonstrate detectable neutralizing antibody titers at six months following the primary series. While the clinical significance of this is unclear, waning antibodies may indicate susceptibility to SARS-CoV-2 infection, while still being protected against severe outcomes.
- In Canada, outbreaks in LTC homes, as well as confirmed cases and COVID-19 associated deaths amongst LTC residents have been increasing in the past several weeks, particularly in jurisdictions experiencing increased community transmission, although it is unclear to what extent this is being driven by unvaccinated residents and/or LTC staff, waning protection in LTC residents, and/or recent onset of the fourth wave of the pandemic, fuelled by a more transmissible strain (Delta) of SARS-CoV-2.
- Unvaccinated individuals in this population are at the highest risk of severe outcomes due to SARS-CoV-2 infection, and therefore it remains critical to ensure LTC residents and seniors living in other congregate settings receive their complete primary vaccine series. It is also very important that healthcare workers providing care, staff, volunteers, visitors, and other close contacts of LTC residents be fully vaccinated with a primary series to protect these residents from infection and from the indirect consequences of COVID-19 outbreaks in these settings.
- While there are no data for LTC residents and limited data available for older adults, early results from studies on mRNA booster doses show a safety profile comparable to that of the second dose of the primary series, and evidence of boosted immune responses and increased short-term vaccine effectiveness in the overall study populations.
- In studies that have included both mRNA vaccines, findings suggest the full dose (100 mcg) of Moderna Spikevax may produce a greater immune response and potentially better effectiveness compared to Pfizer-BioNTech Comirnaty in this population, but investigations are preliminary and ongoing.
- For LTC residents and seniors living in other congregate settings receiving their primary series, an interval that is longer than the manufacturer-recommended intervals between dose 1 and 2 for mRNA vaccines may offer more robust and durable vaccine protection.
- If a longer interval between doses in the primary series or between the primary series and the booster dose is being considered, then risk factors for exposure (including local epidemiology and circulation of VOC) and risk of severe disease should also be taken into account as this could leave individuals susceptible to SARS-CoV-2 infection while waiting to complete the primary series or receive the booster dose.
- NACI is continuing to monitor the evidence related to waning immunity and to discuss the need for booster doses of vaccine for other key populations prioritized for early vaccination (e.g. older adults), as well as for the general population, and will update guidance as required.
Refer to Recommendations on the use of COVID-19 vaccines for further information on COVID-19 vaccines.
Refer to NACI’s Guidance on the prioritization of key populations for COVID-19 immunization for further information on NACI’s initial framework and foundational elements guiding ethical decision-making.
What is the optimal product, vaccine dose, interval between doses, interval between the primary series and additional/booster dose, and potential need for (and frequency of) future booster doses for LTC residents and older adults in congregate living settings to ensure protection against SARS-CoV-2?
What is the efficacy/effectiveness of booster doses in LTC residents and seniors living in other congregate settings, including against:
- symptomatic infection
- severe disease
What are the risks associated with providing a booster dose earlier than necessary?
What is the efficacy, effectiveness, immunogenicity and safety of an additional/booster dose of COVID-19 vaccine against SARS-CoV-2 VOC?
Will special adverse events that have been associated with the primary series (e.g., myocarditis/pericarditis) also be associated with additional/booster doses?
Additional research priorities are listed in NACI’s statement on Recommendations for the use of COVID-19 vaccines.
- Footnote 1
Clarke J. Impacts of the COVID-19 pandemic in nursing and residential care facilities in Canada [Internet]. Ottawa (ON): Statistics Canada; 2021 Jun 10 [cited 2021 Sep 10]. Available from: https://www150.statcan.gc.ca/n1/pub/45-28-0001/2021001/article/00025-eng.htm.
- Footnote 2
Canadian Institute for Health Information (CIHI). The impact of COVID-19 on long-term care in Canada focus on the first 6 months [Internet]. Ottawa (ON): CIHI; 2021 [cited 2021 Sep 10]. Available from: https://www.cihi.ca/sites/default/files/document/impact-covid-19-long-term-care-canada-first-6-months-report-en.pdf.
- Footnote 3
Public Health Agency of Canada (PHAC). Canada COVID-19 weekly epidemiology report 29 August to 04 September 2021 (week 35) [Internet]. Ottawa (ON): PHAC; 2021 Sep 10 [cited 2021 Sep 17]. Available from: https://web.archive.org/web/20210910224621/https://www.canada.ca/content/dam/phac-aspc/documents/services/diseases/2019-novel-coronavirus-infection/surv-covid19-weekly-epi-update-20210910-en.pdf.
- Footnote 4
Kang M, Xin H, Yuan J, Ali ST, Liang Z, Zhang J, et al. Transmission dynamics and epidemiological characteristics of Delta variant infections in China. medRxiv. 2021 Aug 13. doi: 10.1101/2021.08.12.21261991.
- Footnote 5
National Advisory Committee on Immunization (NACI) rapid response: Additional dose of COVID-19 vaccine in immunocompromised individuals following 1- or 2- dose primary series [Internet]. Ottawa (ON): Public Health Agency of Canada; 2021 Sep 10 [cited 2021 Sep 21]. Available from: https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci/statement-september-10-2021-additional-dose-covid-19-vaccine-immunocompromised-following-1-2-dose-series.html.
- Footnote 6
Khoury DS, Cromer D, Reynaldi A, Schlub TE, Wheatley AK, Juno JA, et al. Neutralizing antibody levels are highly predictive of immune protection from symptomatic SARS-CoV-2 infection. Nat Med. 2021 Jul;27(7):1205,1211. doi: 10.1038/s41591-021-01377-8.
- Footnote 7
Bar-On YM, Goldberg Y, Mandel M, Bodenheimer O, Freedman L, Kalkstein N, et al. Protection of BNT162b2 vaccine booster against Covid-19 in Israel. N Engl J Med. 2021 Sep 15. doi: 10.1056/NEJMoa2114255.
- Footnote 8
Patalon T, Gazit S, Pitzer VE, Prunas O, Warren JL, Weinberger DM. Short term reduction in the odds of testing positive for SARS-CoV-2; a comparison between two doses and three doses of the BNT162b2 vaccine. medRxiv. 2021 Aug 31. doi: 10.1101/2021.08.29.21262792.
- Footnote 9
National Institute on Ageing. A cautionary tale: Canada’s vaccine rollout among older adults [Internet]. Toronto (ON): National Institute on Ageing, Ryerson University; 2021 Aug [cited 2021 Sep 15]. Available from: https://static1.squarespace.com/static/5c2fa7b03917eed9b5a436d8/t/61379dbe1d434f27c4a11757/1631034866054/A+Cautionary+Tale+-+Canada%27s+COVID-19+Vaccine+Rollout+for+Older+Canadians.pdf.
- Footnote 10
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: 10.1101/2021.04.23.21256014v2.
- Footnote 11
NIA Long-Term Care COVID-19 Tracker Open Data Working Group. NIA long-term care COVID-19 tracker [Internet]. Toronto (ON): National Institute on Ageing, Ryerson University.; 2021 Sep 14 [cited 2021 Sep 14]. Available from: https://ltc-covid19-tracker.ca/.
- Footnote 12
National Advisory Committee on Immunization (NACI). Guidance on the prioritization of key populations for COVID-19 immunization [Internet]. Ottawa (ON): Public Health Agency of Canada; 2021 Feb [cited 2021 Sep 21]. Available from: https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci/guidance-prioritization-key-populations-covid-19-vaccination.html.
- Footnote 13
Sinha S, Feil C, Iciaszczyk N. The rollout of COVID-19 vaccines in Canadian long-term care homes, 9th April update [Internet]. London: LTC Covid, International Long-term Care Policy Network; 2021 Apr 12 [cited 2021 Sep 21]. Available from: https://ltccovid.org/2021/04/12/the-rollout-of-covid-19-vaccines-in-canadian-long-term-care-homes-9th-april-update/.
- Footnote 14
Public Health Agency of Canada (PHAC). Canada covid-19 weekly epidemiology report: 05 September to 11 September 2021 (week 36) [Internet]. Ottawa (ON): PHAC; 2021 Sep 17 [cited 2021 Sep 21]. Available from: https://web.archive.org/web/20210919004408/https://www.canada.ca/content/dam/phac-aspc/documents/services/diseases/2019-novel-coronavirus-infection/surv-covid19-weekly-epi-update-20210917-en.pdf.
- Footnote 15
Personal communication, re: Canadian data on SARS-CoV-2 case counts and COVID-19 related deaths in long-term care, as per Julie Dunning, National Institute of Ageing. Provided to NACI Secretariat on September 10, 2021.
- Footnote 16
Chemaitelly H, Tang P, Hasan MR, AlMukdad S, Yassine HM, Benslimane FM, et al. Waning of BNT162b2 vaccine protection against SARS-CoV-2 infection in Qatar. medRxiv. 2021 Aug 27. doi: 10.1101/2021.08.25.21262584.
- Footnote 17
Tartof SY, Slezak JM, Fischer H, Hong V, Ackerson BK, Ranasinghe ON, et al. Six-month effectiveness of BNT162B2 mRNA COVID-19 vaccine in a large US integrated health system: A retrospective cohort study. SSRN Preprint. 2021 Aug 23. doi: 10.2139/ssrn.3909743.
- Footnote 18
Goldberg Y, Mandel M, Bar-On Y, Bodenheimer O, Freedman L, Haas EJ, et al. Waning immunity of the BNT162b2 vaccine: A nationwide study from Israel. medRxiv. 2021 Aug 30. doi: 10.1101/2021.08.24.21262423.
- Footnote 19
Cabezas C, Martinez-Marcos M, Coma E, Mora-Fernandez N, Fina F, Fabregas M, et al. Associations of BNT162b2 vaccination with SARS-CoV-2 infection and hospital admission and death with covid-19 in nursing homes and healthcare workers in Catalonia: Prospective cohort study. BMJ. 2021 Aug;374:n1868. doi: 10.1136/bmj.n1868.
- Footnote 20
Monge S, Olmedo C, Alejos B, Lapena MF, Sierra MJ, Limia A. Direct and indirect effectiveness of mRNA vaccination against severe acute respiratory syndrome coronavirus 2 in long-term care facilities, Spain. Emerg Infect Dis. 2021 Oct;27(10):doi: 10.3201/eid2710.211184.
- Footnote 21
Mazagatos C, Vega L, Gallego P, Larrauri A, Monge S, Sierra MJ, et al. Effectiveness of mRNA COVID-19 vaccines in preventing SARS-CoV-2 infections and COVID-19 hospitalisations and deaths in elderly long-term care facility residents, Spain, weeks 53 2020 to 13 2021. Eurosurveillance. 2021;26(24):1,6. doi: 10.2807/1560-7917.ES.2021.26.24.2100452.
- Footnote 22
Martinot M, Carnein S, Kempf C, Gantner P, Gallais F, Fafi-Kremer S. Outbreak of SARS-CoV-2 infection in a long-term care facility after COVID-19 BNT162b2 mRNA vaccination. Clin Microbiol Infect. 2021 Jul 7:S1198-743X(21)00369-4. doi: 10.1016/j.cmi.2021.06.038.
- Footnote 23
Lefèvre B, Tondeur L, Madec Y, Grant R, Lina B, van der Werf S, et al. Impact of B.1.351 (beta) SARS-CoV-2 variant on BNT162b2 mRNA vaccine effectiveness in long-term care facilities of eastern France: a retrospective cohort study. medRxiv. 2021 Jul 31. doi: 10.1101/2021.07.28.21261285.
- Footnote 24
Emborg H, Valentiner-Branth P, Schelde AB, Nielsen KF, Gram MA, Moustsen-Helms I, et al. Vaccine effectiveness of the BNT162b2 mRNA COVID-19 vaccine against RT-PCR confirmed SARS-CoV-2 infections, hospitalisations and mortality in prioritised risk groups. medRxiv. 2021 Jun 2. doi: 10.1101/2021.05.27.21257583.
- Footnote 25
Moustsen-Helms I, Emborg H, Nielsen J, Nielsen KF, Krause TG, Mølbak K, et al. Vaccine effectiveness after 1st and 2nd dose of the BNT162b2 mRNA Covid-19 Vaccine in long-term care facility residents and healthcare workers – a Danish cohort study. medRxiv. 2021 Mar 9. doi: 10.1101/2021.03.08.21252200.
- Footnote 26
Starrfelt J, Danielsen AS, Kacelnik O, Børseth AW, Seppälä E, Meijerink H. High vaccine effectiveness against COVID-19 infection and severe disease among residents and staff of long-term care facilities in Norway, November – June 2021. medRxiv. 2021 Aug 9. doi: 10.1101/2021.08.08.21261357.
- Footnote 27
Cavanaugh AM, Fortier S, Lewis P, Arora V, Johnson M, George K, et al. COVID-19 outbreak associated with a SARS-CoV-2 R.1 lineage variant in a skilled nursing facility after vaccination program - Kentucky, March 2021. MMWR Morb Mortal Wkly Rep. 2021 Apr 30;70(17):639,643. doi: 10.15585/mmwr.mm7017e2.
- Footnote 28
Nanduri S, Pilishvili T, Derado G, Soe MM, Dollard P, Wu H, et al. Effectiveness of Pfizer-BioNTech and Moderna vaccines in preventing SARS-CoV-2 infection among nursing home residents before and during widespread circulation of the SARS-CoV-2 B.1.617.2 (Delta) variant - National Healthcare Safety Network, March 1-August 1, 2021. MMWR Morb Mortal Wkly Rep. 2021;70(34):1163,1166. doi: 10.15585/mmwr.mm7034e3.
- Footnote 29
Williams C, Al-Bargash D, Macalintal C, Stuart R, Seth A, Latham J, et al. COVID-19 outbreak associated with a SARS-CoV-2 P.1 lineage in a long-term care home after implementation of a vaccination program - Ontario, April-May 2021. Clin Infect Dis. 2021 Jul 8:ciab617. doi: 10.1093/cid/ciab617.
- Footnote 30
Breznik JA, Zhang A, Huynh A, Miller MS, Nazy I, Bowdish DME, et al. Antibody responses 3-5 months post-vaccination with mRNA-1273 or BNT163b2 in nursing home residents. medRxiv. 2021 Aug 19. doi: 10.1101/2021.08.17.21262152.
- Footnote 31
Abe KT, Hu Q, Mozafarihashjin M, Samson R, Manguiat K, Robinson A, et al. Neutralizing antibody responses to SARS-CoV-2 variants in vaccinated Ontario long-term care home residents and workers. medRxiv. 2021 Aug 27. doi: 10.1101/2021.08.06.21261721.
- Footnote 32
Brockman MA, Mwimanzi FM, Lapointe HR, Sang Y, Agafitei O, Cheung P, et al. Reduced magnitude and durability of humoral immune responses by COVID-19 mRNA vaccines among older adults. medRxiv. 2021 Sep 12. doi: 10.1101/2021.09.06.21263149.
- Footnote 33
Joint Committee on Vaccination and Immunisation (JCVI). JCVI statement regarding a COVID-19 booster vaccine programme for winter 2021 to 2022 [Internet]. London: Department of Health & Social Care, United Kingdom; 2021 Sep 14 [cited 2021 Sep 21]. Available from: https://www.gov.uk/government/publications/jcvi-statement-september-2021-covid-19-booster-vaccine-programme-for-winter-2021-to-2022/jcvi-statement-regarding-a-covid-19-booster-vaccine-programme-for-winter-2021-to-2022.
- Footnote 34
National Advisory Committee on Immunization (NACI). Recommendations on the use of COVID-19 vaccines [Internet]. Ottawa (ON): Public Health Agency of Canada; 2021 Jul [cited 2021 Sep 21]. Available from: https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci/recommendations-use-covid-19-vaccines.html#a4.
- Footnote 35
Ismail SJ, Hardy K, Tunis MC, Young K, Sicard N, Quach C. A framework for the systematic consideration of ethics, equity, feasibility, and acceptability in vaccine program recommendations. Vaccine. 2020 Aug 10;38(36):5861,5876. doi: 10.1016/j.vaccine.2020.05.051.
- Footnote 36
Ismail SJ, Tunis MC, Zhao L, Quach C. Navigating inequities: a roadmap out of the pandemic. BMJ Glob Health 2021 Jan;6(1):e004087. doi: 10.1136/bmjgh-2020-004087.
- Footnote 37
Ismail SJ, Zhao L, Tunis MC, Deeks SL, Quach C, National Advisory Committee on Immunization. Key populations for early COVID-19 immunization: preliminary guidance for policy. CMAJ. 2020 Nov 30;192(48):E1620,E1632. doi: 10.1503/cmaj.202353.
- Footnote 38
National Advisory Committee on Immunization. Preliminary guidance on key populations for early COVID-19 immunization [Internet]. Ottawa (ON): Public Health Agency of Canada; 2020 Nov [cited 2021 Sep 21]. Available from: https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci/guidance-key-populations-early-covid-19-immunization.html.
- Footnote 39
National Advisory Committee on Immunization. Guidance on the prioritization of initial doses of COVID-19 vaccine(s) [Internet]. Ottawa (ON): Public Health Agency of Canada; 2020 Dec [cited 2021 Sep 21]. Available from: https://www.canada.ca/en/public-health/services/immunization/national-advisory-committee-on-immunization-naci/guidance-prioritization-initial-doses-covid-19-vaccines.html.
- Footnote 40
Long-term care and COVID-19: Report of a Special Task Force prepared for the Chief Science Advisor of Canada. Summer 2020 [Internet]. Ottawa (ON): Office of the Chief Science Advisor; 2020 Oct [cited 2021 Sep 17]. Available from: https://www.ic.gc.ca/eic/site/063.nsf/eng/h_98049.html.
- Footnote 41
Parry H, Bruton R, Stephens C, Brown K, Amirthalingam G, Hallis B, et al. Extended interval BNT162b2 vaccination enhances peak antibody generation in older people. medRxiv. 2021 May 17. doi: 10.1101/2021.05.15.21257017.
- Footnote 42
Amirthalingam G, Bernal JL, Andrews NJ, Whitaker H, Gower C, Stowe J, et al. Higher serological responses and increased vaccine effectiveness demonstrate the value of extended vaccine schedules in combatting COVID-19 in England. medRxiv. 2021 Jul 28. doi: 10.1101/2021.07.26.21261140.
- Footnote 43
Andrews N, Tessier E, Stowe J, Gower C, Kirsebom F, Simmons R, et al. Vaccine effectiveness and duration of protection of Comirnaty, Vaxzevria and Spikevax against mild and severe COVID-19 in the UK. medRxiv. 2021 Sep 21. doi: 10.1101/2021.09.15.21263583.
- Footnote 44
Voysey M, Costa Clemens SA, Madhi SA, Weckx LY, Folegatti PM, Aley PK, et al. Single-dose administration and the influence of the timing of the booster dose on immunogenicity and efficacy of ChAdOx1 nCoV-19 (AZD1222) vaccine: a pooled analysis of four randomised trials. Lancet. 2021 Mar 6;397(10277):881,891. doi: 10.1016/S0140-6736(21)00432-3.
- Footnote 45
ClinicalTrials.gov. Bethesda (MD): National Library of Medicine (US). 2000 Feb 29 -. Identifier: NCT04889209, Delayed heterologous SARS-CoV-2 vaccine dosing (boost) after receipt of EUA vaccines. Sponsor: National Institute of Allergy and Infectious Diseases (NIAID) [Internet].; 2021 Sep 22 [cited 2021 Sep 22]. Available from: https://clinicaltrials.gov/ct2/show/NCT04889209.
- Footnote 46
COV-BOOST. A randomised, phase II UK multi-centre study to determine reactogenicity and immunogenicity of booster vaccination against ancestral and novel variants of SARS-CoV-2 [study protocol] [Internet]. Southampton: University Hospital Southampton NHS Foundation Trust; 2021 Jun 14 [cited 2021 Sep 22]. Available from: https://www.covboost.org.uk/files/cov-boostprotocolv3214jun2021cleanpdf.
- Footnote 47
Puranik A, Lenehan PJ, Silvert E, Niesen MJM, Corchado-Garcia J, O’Horo JC, et al. Comparison of two highly-effective mRNA vaccines for COVID-19 during periods of Alpha and Delta variant prevalence. medRxiv. 2021 Aug 9. doi: 10.1101/2021.08.06.21261707:2021.08.06.21261707.
- Footnote 48
Nasreen S, Chung H, He S, Brown KA, Gubbay JB, Buchan SA, et al. Effectiveness of COVID-19 vaccines against variants of concern in Ontario, Canada. medRxiv. 2021 Jul 16. doi: 10.1101/2021.06.28.21259420.
- Footnote 49
Tang P, Hasan MR, Chemaitelly H, Yassine HM, Benslimane FM, Khatib HAA, et al. BNT162b2 and mRNA-1273 COVID-19 vaccine effectiveness against the Delta (B.1.617.2) variant in Qatar. medRxiv. 2021 Aug 11. doi: 10.1101/2021.08.11.21261885.
- Footnote 50
Vaccines and Related Biological Products Advisory Committee Meeting. September 17, 2021. FDA Briefing Document. Application for licensure of a booster dose for COMIRNATY (COVID-19 Vaccine, mRNA) [Internet]. Silver Spring (MD): U.S. Food and Drug Administration; 2021 Sep [cited 2021 Sep 22]. Available from: https://www.fda.gov/media/152176/download.
This statement was prepared by: E Wong, N Forbes, B Warshawsky, J Montroy, K Farrah, R Krishnan, R Pless, J Zafack, E Abrams, S Ismail, K Young, M Tunis, R Harrison and S Deeks on behalf of NACI.
NACI gratefully acknowledges the contribution of: K Ramotar, N St-Pierre, A Jirovec, SH Lim, N Alluqmani, NACI Secretariat, and the Public Health Ethics Consultative Group.
NACI members: S Deeks (Chair), R Harrison (Vice-Chair), J Bettinger, N Brousseau, P De Wals, E Dubé, V Dubey, K Hildebrand, K Klein, J Papenburg, A Pham-Huy, C Rotstein, B Sander, S Smith, and S Wilson.
Liaison representatives: LM Bucci (Canadian Public Health Association), E Castillo (Society of Obstetricians and Gynaecologists of Canada), A Cohn (Centers for Disease Control and Prevention, United States), L Dupuis (Canadian Nurses Association), J Emili (College of Family Physicians of Canada), D Fell (Canadian Association for Immunization Research and Evaluation), M Lavoie (Council of Chief Medical Officers of Health), D Moore (Canadian Paediatric Society), M Naus (Canadian Immunization Committee), P Emberley (Canadian Pharmacists Association), L Bill (Canadian Indigenous Nurses Association), and S Funnel (Indigenous Physicians Association of Canada).
Ex-officio representatives: V Beswick-Escanlar (National Defence and the Canadian Armed Forces), E Henry (Centre for Immunization and Respiratory Infectious Diseases (CIRID), PHAC), M Lacroix (Public Health Ethics Consultative Group, PHAC), C Lourenco (Biologic and Radiopharmaceutical Drugs Directorate, Health Canada), S Ogunnaike-Cooke (CIRID, PHAC), K Robinson (Marketed Health Products Directorate, HC), G Poliquin (National Microbiology Laboratory, PHAC), and T Wong (First Nations and Inuit Health Branch, Indigenous Services Canada).
NACI High Consequence Infectious Disease Working Group
Members: R Harrison (Chair), Y-G Bui, S Deeks, K Dooling, K Hildebrand, M Miller, M Murti, J Papenburg, R Pless, S Ramanathan, N Stall, and S Vaughan.
PHAC participants: N Abraham, L Coward, N Forbes, C Jensen, A Killikelly, R Krishnan, J Montroy, A Nam, M Patel, M Salvadori, A Sinilaite, R Stirling, E Tice, B Warshawsky, R Ximenes MW Yeung, and J Zafack.
- Confidence interval
- Coronavirus disease 2019
- Ethics, Equity, Feasibility and Acceptability
- Long-term care
- messenger ribonucleic acid
- National Advisory Committee on Immunization
- National Institute on Ageing
- Public Health Agency of Canada
- Public Health Ethics Consultative Group
- Severe acute respiratory syndrome coronavirus 2
- Vaccine effectiveness
- Variant on concern
A rapid literature review of VE following a primary COVID-19 vaccine series in LTC residents and seniors living in other congregate settings identified 11 observational studies from six different countries (Spain n=3Footnote 19Footnote 20Footnote 21; France n=2Footnote 22Footnote 23; Denmark n=2Footnote 24Footnote 25; Norway n=1Footnote 26; USA n=2Footnote 27Footnote 28; Canada n=1Footnote 29, and included over 750,000 residents. Ten studies reported exclusively on mRNA vaccinesFootnote 19Footnote 20Footnote 21Footnote 22Footnote 23Footnote 24Footnote 25Footnote 27Footnote 28Footnote 29, while one study also included a minority of participants who received AstraZeneca Vaxzevria or mixed vaccine schedulesFootnote 26. All studies that reported interval between doses (10 of 11 studies) used the manufacturer recommend interval. Seven of the included studies were large, population-based studiesFootnote 19Footnote 20Footnote 21Footnote 24Footnote 25Footnote 26Footnote 28, while the remaining four studies were specific to one or two LTC residences experiencing outbreaksFootnote 22Footnote 23Footnote 27Footnote 29.
All 11 studies reported VE against confirmed SARS-CoV-2 infection (symptomatic or asymptomatic), which ranged from 49% to 91%, with significant heterogeneity in effect size. However, even with the large variation in effect size seen with VE against confirmed infection, VE against hospitalization from COVID-19 was high in all four studies reporting this outcome (ranging from 75% to 95%)Footnote 19Footnote 21Footnote 24Footnote 27, as was VE against death from COVID-19 (ranging from 89% to 97%) in five studiesFootnote 19Footnote 21Footnote 24Footnote 26Footnote 27. Studies reporting VE against hospitalization or VE against death completed follow-up between March and May or March and June, respectively. Only one studyFootnote 28 was performed during the period of time where the B.1.617.2 (Delta) variant was the predominately circulating VOC. This study demonstrated a significant decline in VE against symptomatic infection during this time, when compared to the “pre-Delta” period of time (from 74.7% in March – May 2021 to 53.1% from June 21 – August 1 2021)Footnote 28.
Due to limited evidence and differences in study observation periods it is difficult to draw conclusions on waning VE over time in LTC residents and seniors living in other congregate settings. VE by time since second dose of COVID-19 vaccine could not be determined in the studies as no study estimated VE by time since last dose. The overall certainty of evidence was graded very low for all assessed outcomes, due to the observational design of all included studies, as well as concerns regarding the risk of bias of many included studies.
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