Archive 49: Guidance on COVID-19 vaccine booster doses: Initial considerations for 2023 [2023-01-20]

Publication date: January 20, 2023

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Organization: Public Health Agency of Canada

Cat.: HP5-152/1-2023E-PDF

ISBN: 978-0-660-47070-2

Pub.: 220696

Published: 2023-01-20

Notice to reader

This is an archived version. Please refer to current COVID-19 vaccine pages:

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Preamble

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.

Background

The Omicron variant of SARS-CoV-2 virus was first detected in November 2021, with its sub-variants continuing to circulate in Canada and globally, more than one year later. The epidemiology of COVID-19 is expected to continue to evolve, and the likelihood, timing, and severity of any potential future resurgence of COVID-19 is uncertain. No strong evidence of seasonality of COVID-19 has emerged to date, and it has yet to be seen whether the incidence of SARS-CoV-2 virus infections will be analogous to other respiratory viruses that increase in the fall and winter seasons, thereby increasing pressure on health systems during this period.
Since September 2021, NACI has been developing and updating guidance on the use of COVID-19 booster doses based on a decision-making framework assessing the need for, and benefit of, additional doses of COVID-19 vaccines in various populations. These decisions were supported by vaccine principles, as well as evidence where available.

The NACI Interim guidance on planning considerations for a fall 2022 COVID-19 vaccine booster program in Canada (June 29, 2022) provided jurisdictions with planning advice for a booster dose program in advance of a possible future surge of COVID-19 in Canada over the fall and winter months and included an updated decision-making framework on booster doses. More specific guidance on vaccination recommendations for the fall of 2022, including booster doses in children 5 to 11 years of age and the use of bivalent Omicron-containing mRNA COVID-19 vaccines, was provided in the following NACI statements:

Since then, additional NACI guidance has been requested as provinces and territories begin to consider planning for 2023.

NACI's recommendations remain aligned with the current goals of the Canadian COVID-19 Pandemic Response (as of February 14, 2022):

For further information on NACI's recommendations on the use of COVID-19 vaccines, please refer to National Advisory Committee on Immunization (NACI): Statements and publications and the COVID-19 vaccine chapter in the Canadian Immunization Guide (CIG).

Methods

On November 29, 2022, and December 13, 2022, the NACI COVID-19 Working Group and full NACI membership respectively reviewed the available evidence on epidemiology and vaccine protection, as well as planning considerations for the next steps of the COVID-19 booster program, including ethics, equity, feasibility and acceptability considerations. NACI also recommended the continued application of the existing decision-making framework for booster doses. NACI approved these recommendations on January 06, 2023.

Further information on NACI's process and procedures is available elsewhereFootnote 1 Footnote 2.

Key considerations for booster dose decisions

The following sections outline key considerations to monitor over time with regard to future booster dose recommendations, as reflected in NACI's decision-making framework on booster doses. Available information as of December 19, 2022 is summarized below.

Epidemiology

Duration of protection from booster doses against severe outcomes due to COVID-19

Hybrid immunity

Immunogenicity and VE of booster doses of Omicron-containing bivalent mRNA COVID-19 vaccine

Ethics, equity, feasibility and acceptability

Recommendations

At this time, NACI is reinforcing existing recommendations for COVID-19 vaccines including suggested timing of doses following a previous SARS-CoV-2 infection. The fall 2022 booster program is being used as the reference point to consolidate booster guidance that has been published to date. A summary of recommendations for the primary series and booster doses is also provided in Table 1.

It is noted that the start date of the fall 2022 booster program varied across Canadian jurisdictions from August to September 2022.

Please see Table 2 for an explanation of strong versus discretionary NACI recommendations.

NACI continues to recommend a COVID-19 vaccine primary series as follows:

  1. Individuals 5 years of age and older should be immunized with a primary series of an authorized mRNA vaccine. (Strong NACI recommendation)
  2. Children 6 months to under 5 years of age may be immunized with a primary series of an authorized mRNA vaccine. (Discretionary NACI recommendation)

Additional details including those pertaining to alternative vaccine products are available in the COVID-19 vaccine chapter in the Canadian Immunization Guide and NACI statements and publications.

NACI continues to recommend COVID-19 vaccine booster doses as follows:

  1. At least one booster dose should be offered to all adults 18 years of age and over and adolescents 12 to 17 years of age who are at increased risk of severe illness. (Strong NACI recommendation)
    • This recommendation predates guidance issued in the fall of 2022. The individuals identified above who have not yet received any booster dose should receive one.
  2. All adults 65 years of age and older, and individuals 5 to 64 years of age who are at increased risk of severe illness from COVID-19 should have received a booster dose since the start of fall 2022. For individuals who have not yet received the fall 2022 booster dose, it should be offered, as per the recommended intervals (see recommendation #7). (Strong NACI recommendation)
    • Individuals 12 years of age and older who are considered at increased risk of severe illness from COVID-19 include those with underlying medical conditions (including those who are moderately to severely immunocompromised and who therefore received a three-dose primary series), and racialized and marginalized populations who have been disproportionately affected due to a number of intersecting factors. Other groups considered at increased risk are identified in NACI's Interim guidance on planning considerations for a fall 2022 COVID-19 vaccine booster program in Canada.
    • There is limited evidence on clinical risk factors for severe COVID-19 disease in pediatric populations younger than 12 years of age. Children at increased risk for severe outcomes may include children: with obesity, who are medically fragile/have medical complexities, who have more than one comorbidity or neurological disorders, or who have Down syndrome or immunocompromising conditions.
  3. In addition, a booster dose may be offered to individuals 5 to 64 years of age without risk factors for severe illness from COVID-19 if one has not already been received since the start of fall 2022. For individuals who have not yet received a fall 2022 booster dose, it may be offered, as per the recommended intervals (see recommendation #7). (Discretionary NACI recommendation)
  4. There are no authorized booster dose products for children 6 months to under 5 years of age at this time. NACI has not issued recommendations on booster doses for this age group.
  5. When COVID-19 booster doses are offered, they should be provided using the recommended interval of 6 or more months since the previous COVID-19 vaccine dose or SARS-CoV-2 infection (whichever is later), as more time between exposures to vaccine or infection may result in a better immune response.
  6. Bivalent Omicron-containing mRNA COVID-19 vaccines are the preferred booster products for all individuals 5 years of age and older.
    • Since October 2022, NACI has recommended that bivalent Omicron-containing mRNA COVID-19 vaccines are the preferred booster products for the authorized age groups (at the time, the bivalent vaccine was authorized for individuals 12 years of age and older). This authorization was expanded to all individuals 5 years of age and older following Health Canada's authorization of the bivalent Pfizer-BioNTech Comirnaty mRNA 10 microgram product for children 5 to 11 years of age in December 2022.
    • The first booster dose program for children 5 to 11 years of age coincided with the fall booster dose campaign that targeted individuals 12 years of age and older. To integrate booster dose guidance for both of these age groups, current booster dose recommendations for individuals 5 years of age and older are summarized in Table 1. Children 5 to 11 years of age are recommended to receive only one booster dose at this time. However, at the provider's discretion, an additional booster dose using the bivalent vaccine (as per the recommended interval – see recommendation #7) could be offered to children considered at high risk of severe COVID-19 who have previously received a fall booster dose with the original Pfizer-BioNTech Comirnaty mRNA vaccine.
Table 1. Summary table of mRNA COVID-19 vaccine recommendations by age group
Population by age NACI recommendation
Primary series Booster dose(s)Footnote a Footnote b

Adults 65 years of age and older

Should be offeredFootnote c

At least one booster dose continues to be recommended for all adults 18 years of age and over.

Regardless of previous booster doses, a booster since the start of fall 2022 should be offered as per the recommended intervalFootnote b if not already received.

Adults 18 to 64 years of age

Should be offeredFootnote c

Those at increased risk for severe illness from COVID-19:

At least one booster dose continues to be recommended for all adults 18 years of age and over.

Regardless of previous booster doses, a booster since the start of fall 2022 should be offered as per the recommended intervalFootnote b if not already received.

Those NOT at increased risk for severe illness from COVID-19:

At least one booster dose continues to be recommended for all adults 18 years of age and over.

A booster since the start of fall 2022 may be offered as per the recommended intervalFootnote b if not already received.

Adolescents 12 to 17 years of age

Should be offeredFootnote c

Those at increased risk for severe illness from COVID-19:

At least one booster dose continues to be recommended for adolescents 12 to 17 years of age who are at increased risk of severe illness from COVID-19.

Regardless of previous booster doses, a booster since the start of fall 2022 should be offered as per the recommended intervalFootnote b if not already receivedFootnote d.

Those NOT at increased risk for severe illness from COVID-19:

A booster since the start of fall 2022 may be offered as per the recommended intervalFootnote b if not already received.

Children 5 to 11 years of age

Should be offeredFootnote c

Those at increased risk for severe illness from COVID-19:

A booster since the start of fall 2022 should be offered as per the recommended intervalFootnote b if not already receivedFootnote d.

Those NOT at increased risk for severe illness from COVID-19:

A booster since the start of fall 2022 may be offered as per the recommended intervalFootnote b if not already received.

Children 6 months to less than 5 years of age

May be offeredFootnote c

No authorized product; not recommended

Footnote a

Bivalent Omicron-containing products are preferred for booster doses for the authorized ages.

Return to footnote a referrer

Footnote b

The recommended interval between the previous COVID-19 vaccine dose (previous booster or completion of the primary series) and a booster dose is 6 months, and between infection and a booster dose is 6 months (whichever is longer). A shorter interval of at least 3 months may be considered in the context of heightened epidemiologic risk, evolving SARS-COV-2 epidemiology, as well as operational considerations for efficient deployment.

Return to footnote b referrer

Footnote c

Those who are moderately to severely immunocompromised are recommended to receive an additional dose in the primary series.

Return to footnote c referrer

Footnote d

Children 5 to 11 years of age who already received a booster dose with an original COVID-19 mRNA vaccine are not recommended to receive a bivalent Omicron-containing booster. However, at the provider's discretion, a bivalent booster dose (as per the recommended intervalFootnote b) could be offered to children considered at high risk of severe COVID-19 who have previously received a booster dose with the original Pfizer-BioNTech Comirnaty mRNA vaccine.

Return to footnote d referrer

Additional details are available in the COVID-19 vaccine chapter in the Canadian Immunization Guide and NACI statements and publications.

Considerations regarding potential future booster programs and planning

With the inherent uncertainties around the evolution of the pandemic, it is unclear when the need for additional COVID-19 vaccine booster doses will arise, or to whom booster doses should be offered in the event that they are needed. NACI will continue to monitor the evidence, including SARS-CoV-2 epidemiology and duration of vaccine protection, particularly with regard to severe outcomes, in the coming months to provide recommendations on the timing of subsequent booster doses if warranted. Product options for booster doses could include additional vaccines as they become available.

There are a number of options for the timing of possible future booster doses if additional booster doses are required, and these include the following:

In addition to monitoring epidemiology, duration of protection from current booster doses and previous infection, safety, immunogenicity, and vaccine effectiveness of bivalent Omicron-containing vaccines or alternative vaccine products, future booster dose decisions should consider ethics, equity, and acceptability of future booster dose recommendations in addition to feasibility considerations of delivering booster dose campaigns. NACI acknowledges that significant preparations occur every year for the seasonal influenza campaign and will endeavour to provide further advice to inform the potential integration of COVID-19 immunization in advance of the fall of 2023.

Research priorities

  1. Continuous monitoring of data on the safety, immunogenicity, efficacy, and effectiveness of COVID-19 vaccines, including booster doses, through clinical trials and studies in real-world settings, including the degree and duration of protection conferred by each booster dose against circulating variants. The research should also consider the clinical implications of previous SARS-CoV-2 infection; repeated immunization; and outcomes after any infection such as MIS-C, post-COVID-19 condition/post-acute COVID syndrome (long COVID), or infection-induced myocarditis or pericarditis in adult, adolescent, and pediatric populations.
  2. Further evaluations of the optimal interval between dose administration, as well as further evaluations of the optimal interval between previous SARS-CoV-2 infection and vaccine dose administration.
  3. Vigilant monitoring and reporting of adverse events of special interest, including myocarditis and/or pericarditis, in order to accurately inform potential risks associated with any future booster doses. Global collaboration should be prioritized to enable data sharing so decision makers around the world can weigh benefits and risks of additional booster doses of COVID-19 vaccines.
  4. Continuous monitoring of COVID-19 epidemiology and VE in special populations at high risk of severe outcomes or long-term consequences of infection with COVID-19.
  5. Further evaluation on the optimal timing and trigger for the initiation of potential future booster dose recommendations, as well as evaluation of potential risks associated with providing booster doses earlier than necessary.
  6. Continuous monitoring of vaccine coverage in Canada, for COVID-19 vaccines and other routine vaccines, particularly in the context of COVID-19 vaccine booster doses and including consideration of measures that may reduce the risk of disparities in vaccine confidence and uptake across different sub-populations.
Table 2. Strength of NACI recommendations
Strength of NACI recommendation
based on factors not isolated to strength of evidence
(e.g., public health need)
Strong Discretionary

Wording

"should/should not be offered"

"may/may not be offered"

Rationale

Known/anticipated advantages outweigh known/anticipated disadvantages ("should"),
Or
Known/Anticipated disadvantages outweigh known/anticipated advantages ("should not")

Known/anticipated advantages are closely balanced with known/anticipated disadvantages,
Or
Uncertainty in the evidence of advantages and disadvantages exists

Implication

A strong recommendation applies to most populations/individuals and should be followed unless a clear and compelling rationale for an alternative approach is present.

A discretionary recommendation may be considered for some populations/individuals in some circumstances. Alternative approaches may be reasonable.

Acknowledgments

This statement was prepared by: E Wong, B Warshawsky, SJ Ismail, MC Tunis, R Harrison, S Wilson, and S Deeks, on behalf of NACI.

NACI gratefully acknowledges the contribution of: K Ramotar, C Mauviel, M Salvadori, J Zafack, N Forbes, R Krishnan, J Montroy, A Killikelly, E Tice, and the NACI Secretariat.

NACI members: S Deeks (Chair), R Harrison (Vice-Chair), M Andrew, J Bettinger, N Brousseau, H Decaluwe, P De Wals, E Dubé, V Dubey, K Hildebrand, K Klein, J Papenburg, A Pham-Huy, B Sander, S Smith, and S Wilson.

Liaison representatives: L Bill / M Nowgesic (Canadian Indigenous Nurses Association), LM Bucci (Canadian Public Health Association), E Castillo (Society of Obstetricians and Gynaecologists of Canada), J MacNeil (Centers for Disease Control and Prevention, United States), J Comeau (Association of Medical Microbiology and Infectious Disease Canada), M Osmack (Indigenous Physicians Association of Canada), J Hu (College of Family Physicians of Canada), M Lavoie (Council of Chief Medical Officers of Health), D Moore (Canadian Paediatric Society), M Naus (Canadian Immunization Committee), A Ung (Canadian Pharmacists Association).

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), P Fandja (Marketed Health Products Directorate, Health Canada), D MacDonald (COVID-19 Epidemiology and Surveillance, PHAC), S Ogunnaike-Cooke (CIRID, PHAC), C Pham (Biologic and Radiopharmaceutical Drugs Directorate, Health Canada), M Routledge (National Microbiology Laboratory, PHAC), and T Wong (First Nations and Inuit Health Branch, Indigenous Services Canada).

NACI COVID-19 Vaccine Working Group

Members: S Wilson (Chair), M Adurogbangba, M Andrew, Y-G Bui, H Decaluwe, P De Wals, V Dubey, S Hosseini-Moghaddam, M Miller, D Moore, S Oliver, and E Twentyman.

PHAC Participants: NK Abraham, O Baclic, L Coward, P Doyon-Plourde, N Forbes, M Hersi, N Islam, SJ Ismail, C Jensen, CY Jeong, F Khan, A Killikelly, R Krishnan, SH Lim, N Mohamed, J Montroy, S Pierre, R Pless, M Salvadori, A Stevens, E Tice, A Tuite, MC Tunis, E Wong, R Ximenes, MW Yeung, and J Zafack.

References

Footnote 1

Ismail SJ, Langley JM, Harris TM, Warshawsky BF, Desai S, FarhangMehr M. Canada's National Advisory Committee on Immunization (NACI): Evidence-based decision-making on vaccines and immunization. Vaccine. 2010;28:A58,63. doi: 10.1016/j.vaccine.2010.02.035.

Return to footnote 1 referrer

Footnote 2

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.

Return to footnote 2 referrer

Footnote 3

Grewal R, Nguyen L, Buchan SA, Wilson SE, Nasreen S, Austin PC, et al. Effectiveness of mRNA COVID-19 vaccine booster doses against Omicron severe outcomes. medRxiv. 2022 Nov 01. https://doi.org/10.1101/2022.10.31.22281766.

Return to footnote 3 referrer

Footnote 4

Altarawneh HN, Chemaitelly H, Ayoub HH, Tang P, Hasan MR, Yassine HM, et al. Effects of Previous Infection and Vaccination on Symptomatic Omicron Infections. N Engl J Med. 2022 Jul 7;387(1):21,34. doi: 10.1056/NEJMoa2203965.

Return to footnote 4 referrer

Footnote 5

Carazo S, Skowronski DM, Brisson M, Barkati S, Sauvageau C, Brousseau N, et al. Protection against Omicron BA.2 reinfection conferred by primary Omicron or pre-Omicron infection with and without mRNA vaccination. medRxiv. 2022 Jun 27. https://doi.org/10.1101/2022.06.23.22276824.

Return to footnote 5 referrer

Footnote 6

Cerqueira-Silva T, de Araujo Oliveira V, Paixão ES, Florentino PTV, Penna GO, Pearce N, et al. Vaccination plus previous infection: protection during the omicron wave in Brazil. Lancet Infect Dis. 2022 May 16. doi: 10.1016/S1473-3099(22)00288-2.

Return to footnote 6 referrer

Footnote 7

Chin ET, Leidner D, Lamson L, Lucas K, Studdert DM, Goldhaber-Fiebert JD, et al. Protection against Omicron from Vaccination and Previous Infection in a Prison System. N Engl J Med. 2022 Nov 10;387(19):1770,1782. doi: 10.1056/NEJMoa2207082.

Return to footnote 7 referrer

Footnote 8

Lind ML, Robertson AJ, Silva J, Warner F, Coppi AC, Price N, et al. Effectiveness of Primary and Booster COVID-19 mRNA Vaccination against Omicron Variant SARS-CoV-2 Infection in People with a Prior SARS-CoV-2 Infection. medRxiv. 2022 Apr 25. https://doi.org/10.1101/2022.04.19.22274056.

Return to footnote 8 referrer

Footnote 9

Spreco A, Dahlström Ö, Jöud A, Nordvall D, Fagerström C, Blomqvist E, et al. Effectiveness of the BNT162b2 mRNA Vaccine Compared with Hybrid Immunity in Populations Prioritized and Non-Prioritized for COVID-19 Vaccination in 2021-2022: A Naturalistic Case-Control Study in Sweden. Vaccines (Basel). 2022 Aug 7;10(8):1273. doi: 10.3390/vaccines10081273.

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Footnote 10

Vicentini M, Venturelli F, Mancuso P, Bisaccia E, Zerbini A, Massari M, et al. Risk of SARS-CoV-2 Reinfection by Vaccination Status, Predominant Variant, and Time from Previous Infection: A Cohort Study in Italy. SSRN. 2022 Jun 09. doi: 10.2139/ssrn.4132329.

Return to footnote 10 referrer

Footnote 11

Veneti L, Berild JD, Watle SV, Starrfelt J, Greve-Isdahl M, Langlete P, et al. Vaccine effectiveness with BNT162b2 (Comirnaty, Pfizer-BioNTech) vaccine against reported SARS-CoV-2 Delta and Omicron infection among adolescents, Norway, August 2021 to January 2022. medRxiv. 2022 Mar 25. https://doi.org/10.1101/2022.03.24.22272854.

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Footnote 12

Gram MA, Emborg H, Schelde AB, Friis NU, Nielsen KF, Moustsen-Helms IR, et al. Vaccine effectiveness against SARS-CoV-2 infection or COVID-19 hospitalization with the Alpha, Delta, or Omicron SARS-CoV-2 variant: A nationwide Danish cohort study. PLoS Med. 2022 Sep 1;19(9):e1003992. doi: 10.1371/journal.pmed.1003992.

Return to footnote 12 referrer

Footnote 13

De Serres G, Febriani Y, Ouakki M, Talbot D, Gilca R, Deceuninck G, et al. Efficacité du vaccin contre la COVID-19 causée par le variant Omicron au Québec Résultats Préliminaires. INSPQ. 2022 Feb 16. Available in French: https://www.inspq.qc.ca/covid-19/vaccination/efficacite-omicron.

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Footnote 14

Link-Gelles R, Levy ME, Gaglani M, Irving SA, Stockwell M, Dascomb K, et al. Effectiveness of 2, 3, and 4 COVID-19 mRNA Vaccine Doses Among Immunocompetent Adults During Periods when SARS-CoV-2 Omicron BA.1 and BA.2/BA.2.12.1 Sublineages Predominated - VISION Network, 10 States, December 2021-June 2022. MMWR Morb Mortal Wkly Rep. 2022 Jul 22;71(29):931,939. doi: 10.15585/mmwr.mm7129e1.

Return to footnote 14 referrer

Footnote 15

Ferdinands JM, Rao S, Dixon BE, Mitchell PK, DeSilva MB, Irving SA, et al. Waning 2-Dose and 3-Dose Effectiveness of mRNA Vaccines Against COVID-19-Associated Emergency Department and Urgent Care Encounters and Hospitalizations Among Adults During Periods of Delta and Omicron Variant Predominance - VISION Network, 10 States, August 2021-January 2022. MMWR Morb Mortal Wkly Rep. 2022 Feb 18;71(7):255,263. doi: 10.15585/mmwr.mm7107e2.

Return to footnote 15 referrer

Footnote 16

Stowe J, Andrews N, Kirsebom F, Ramsay M, Bernal JL. Effectiveness of COVID-19 vaccines against Omicron and Delta hospitalisation, a test negative case-control study. Nat Commun. 2022 Sep 30;13(1):5736. doi: 10.1038/s41467-022-33378-7.

Return to footnote 16 referrer

Footnote 17

Seroprevalence against SARS-CoV-2 due to infection in Canada [Internet]. Ottawa (ON): Covid-19 Immunity Task Force (CITF); 2022 Jul 05 [cited 2022 Dec 19]. Available from: https://www.covid19immunitytaskforce.ca/wp-content/uploads/2022/07/CITF_Bespoke-report_Omicron-tsunami_2022_FINAL_ENG.pdf.

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Footnote 18

Carazo S, Skowronski DM, Brisson M, Barkati S, Sauvageau C, Brousseau N, et al. Protection against omicron (B.1.1.529) BA.2 reinfection conferred by primary omicron BA.1 or pre-omicron SARS-CoV-2 infection among health-care workers with and without mRNA vaccination: a test-negative case-control study. Lancet Infect Dis. 2023 Jan;23(1):45,55. doi: 10.1016/S1473-3099(22)00578-3.

Return to footnote 18 referrer

Footnote 19

Wang Q, Bowen A, Valdez R, Gherasim C, Gordon A, Liu L, et al. Antibody responses to Omicron BA.4/BA.5 bivalent mRNA vaccine booster shot. bioRxiv. 2022 Oct 24. https://doi.org/10.1101/2022.10.22.513349.

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Footnote 20

Collier AY, Miller J, Hachmann NP, McMahan K, Liu J, Bondzie EA, et al. Immunogenicity of the BA.5 Bivalent mRNA Vaccine Boosters. bioRxiv. 2022 Oct 25. https://doi.org/10.1101/2022.10.24.513619.

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Footnote 21

Kurhade C, Zou J, Xia H, Liu M, Chang HC, Ren P, et al. Low neutralization of SARS-CoV-2 Omicron BA.2.75.2, BQ.1.1 and XBB.1 by parental mRNA vaccine or a BA.5 bivalent booster. Nat Med. 2022 Dec 6. doi: 10.1038/s41591-022-02162-x.

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Footnote 22

Davis-Gardner M, Lai L, Wali B, Samaha H, Solis D, Lee M, et al. mRNA bivalent booster enhances neutralization against BA.2.75.2 and BQ.1.1. bioRxiv. 2022 Nov 1. https://doi.org/10.1101/2022.10.31.514636.

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Footnote 23

Wang Q, Iketani S, Li Z, Liu L, Guo Y, Huang Y, et al. Alarming antibody evasion properties of rising SARS-CoV-2 BQ and XBB subvariants. bioRxiv. 2022 Nov 28. https://doi.org/10.1101/2022.11.23.517532.

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Footnote 24

Chalkias S, Harper C, Vrbicky K, Walsh SR, Essink B, Brosz A, et al. A Bivalent Omicron-Containing Booster Vaccine against Covid-19. N Engl J Med. 2022 Oct 06;387:1279,1291. doi: 10.1056/NEJMoa2208343.

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Footnote 25

Zou J, Kurhade C, Patel S, Kitchin N, Tompkins K, Cutler M, et al. Improved Neutralization of Omicron BA.4/5, BA.4.6, BA.2.75.2, BQ.1.1, and XBB.1 with Bivalent BA.4/5 Vaccine. bioRxiv. 2022 Nov 17. https://doi.org/10.1101/2022.11.17.516898.

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Footnote 26

Kwong J, CIRN PCN Ontario team. Personal communication. Effectiveness of monovalent and bivalent mRNA COVID-19 vaccine booster doses against Omicron severe outcomes. 2022 Dec 12.

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Footnote 27

Link-Gelles R, Ciesla AA, Fleming-Dutra KE, Smith ZR, Britton A, Wiegand RE, et al. Effectiveness of Bivalent mRNA Vaccines in Preventing Symptomatic SARS-CoV-2 Infection — Increasing Community Access to Testing Program, United States, September–November 2022. Morbidity and Mortality Weekly Report (MMWR). 2022 Dec 2;71(48):1526,1530. doi: 10.15585/mmwr.mm7148e1.

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Footnote 28

Tenforde MW, Weber ZA, Natarajan K, Klein NP, Kharbanda AB, Stenehjem E, et al. Early Estimates of Bivalent mRNA Vaccine Effectiveness in Preventing COVID-19-Associated Emergency Department or Urgent Care Encounters and Hospitalizations Among Immunocompetent Adults - VISION Network, Nine States, September-November 2022. MMWR Morb Mortal Wkly Rep. 2022 Dec 30;71(5152):1616,1624. doi: 10.15585/mmwr.mm715152e1.

Return to footnote 28 referrer

Footnote 29

Surie D, DeCuir J, Zhu Y, Gaglani M, Ginde AA, Douin DJ, et al. Early Estimates of Bivalent mRNA Vaccine Effectiveness in Preventing COVID-19-Associated Hospitalization Among Immunocompetent Adults Aged ≥65 Years - IVY Network, 18 States, September 8-November 30, 2022. MMWR Morb Mortal Wkly Rep. 2022 Dec 30;71(5152):1625,1630. doi: 10.15585/mmwr.mm715152e2.

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