Archived 50: Guidance on an additional COVID-19 booster dose in the spring of 2023 for individuals at high risk of severe illness due to COVID-19 [2023-03-03]

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Organization: Public Health Agency of Canada

Date published: 2023-03-03

Cat.: HP5-157/1-2023E-PDF
ISBN: 978-0-660-47815-9
Pub.: 220791

Publication date: March 3, 2023

Notice to reader

This is an archived version.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

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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.


On January 20, 2023, NACI published Guidance on COVID-19 vaccine booster doses: Initial considerations for 2023. This guidance consolidated and reinforced previously established booster dose recommendations and extended the fall booster program for those who had not yet received a 2022 recommended booster dose into 2023.

Since that time:

NACI continues to monitor the rapidly evolving scientific data recognizing that the trajectory of the COVID-19 pandemic remains unclear. Updated recommendations will be made as needed.

NACI's recommendations remain aligned with the goals of the Canadian COVID-19 Pandemic Response that were last updated on February 14, 2022:


On February 6 and 7, 2023, NACI reviewed the available epidemiology and evidence on vaccine protection and hybrid immunity, including the performance of bivalent vaccines based on clinical trial data and real-world evidence from observational studies. Preliminary modelling data were also considered, as were ethics and acceptability considerations. NACI continues to apply the decision-making framework for booster doses in their deliberations. NACI approved these recommendations on February 19, 2023.

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)

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

Overview of evidence

Available information as of February 5, 2023, is summarized below.

Evolving epidemiology

Vaccine effectiveness and duration of vaccine protection of mRNA COVID-19 vaccine booster doses

Vaccine protection against infection and symptomatic disease with original monovalent COVID-19 vaccines has been shown to wane over time; however, protection against severe outcomes persists longer than protection against symptomatic disease Footnote 13Footnote 14 Footnote 15Footnote 16 Footnote 17Footnote 18 Footnote 19Footnote 20 Footnote 21Footnote 22 Footnote 23Footnote 24. Evidence suggests that a fourth dose of an original monovalent COVID-19 vaccine provides an increase in vaccine effectiveness (VE) against infection; however, waning of protection is observed over time, consistent with the waning of protection after two or three doses Footnote 25Footnote 26 Footnote 27Footnote 28 Footnote 29Footnote 30. VE against severe disease from booster doses is generally higher and more sustained than against infection. Due to the short follow-up period to date, there are no estimates available regarding waning following bivalent booster doses against infection or severe disease.

Safety of Omicron-containing bivalent mRNA COVID-19 vaccines

Hybrid immunity

Ethics, equity, feasibility, and acceptability (EEFA)

Other considerations


Please see Table 1 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.

  1. For individuals who have not received previously recommended doses (primary series or booster doses, including the fall 2022 booster dose), NACI recommendations are available in Guidance on COVID-19 vaccine booster doses: Initial considerations for 2023.
  2. Starting in the spring of 2023, NACI recommends that an additional booster dose may be offered as per the recommended interval* to the following individuals who are at increased risk of severe illness from COVID-19:
    • Adults 80 years of age and older
    • Adult residents of long-term care homes and other congregate living settings for seniors or those with complex medical care needs
    • Adults 18 years of age and older who are moderately to severely immunocompromised (due to an underlying condition or treatment)
    • Adults 65 to 79 years of age, particularly if they do not have a known prior history of SARS-CoV-2 infection**

      (Discretionary NACI recommendation)

      * The recommended interval is 6 or more months from the last COVID-19 vaccine dose or SARS-CoV-2 infection if applicable (whichever is longer). It should be noted that vaccination with shorter intervals between previous vaccination or infection has not been shown to pose a safety risk, though evidence shows that the antibody response is higher with longer intervals between infection and vaccination and with longer intervals between vaccination doses.

      **Previous infection can be defined in different ways based on jurisdictional policies and access to testing. The following suggestion can be considered to define previous infection with SARS-CoV-2:

    • Confirmed by a molecular (e.g., PCR) or Health Canada-approved antigen detection-based test; or
    • Symptomatic disease compatible with COVID-19 AND household exposure to a confirmed COVID-19 case.

For further information on these recommendations, please refer to the COVID-19 vaccine chapter in the Canadian Immunization Guide (CIG).

NACI continues to monitor and assess the evidence as it emerges and will update its recommendations as needed.

Research priorities

  1. Continuous monitoring of data on the safety, immunogenicity, efficacy, and effectiveness of COVID-19 vaccines, including bivalent mRNA 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 multisystem inflammatory syndrome in children (MIS-C), post-COVID-19 condition/post-acute COVID syndrome (long COVID), or infection-induced myocarditis and/or pericarditis in older adult, 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 to support the rapid identification of potential vaccine safety signals and 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, including but not limited to those with co-morbidities, immunocompromising conditions, and pregnant populations.
  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 1. 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"),
Known/Anticipated disadvantages outweigh known/anticipated advantages ("should not").
Known/anticipated advantages are closely balanced with known/anticipated disadvantages,
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.


This statement was prepared by: E Wong, B Warshawsky, J Montroy, J Zafack, 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, R Krishnan, 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, M O'Driscoll, J Papenburg, A Pham-Huy, B Sander, and S Wilson.

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


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.

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Footnote 3

Chalkias S, Whatley J, Eder F, Essink B, Khetan S, Bradley P, et al. Safety and Immunogenicity of Omicron BA.4/BA.5 Bivalent Vaccine Against Covid-19. medRxiv. 2022 Dec 13.

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Footnote 4

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.

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Footnote 5

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 6

Davis-Gardner ME, Lai L, Wali B, Samaha H, Solis D, Lee M, et al. Neutralization against BA.2.75.2, BQ.1.1, and XBB from mRNA Bivalent Booster. N Engl J Med. 2023 Jan 12;388(2):183,185. doi: 10.1056/NEJMc2214293.

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Footnote 7

Arora P, Cossmann A, Schulz SR, Ramos GM, Stankov MV, Jäck H, et al. Neutralisation sensitivity of the SARS-CoV-2 XBB.1 lineage. Lancet Infect Dis. 2023 Feb;23(2):147,148. doi: 10.1016/S1473-3099(22)00831-3.

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Footnote 8

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. Cell. 2023 Jan 19;186(2):279,286.e8. doi: 10.1016/j.cell.2022.12.018.

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Footnote 9

Uriu K, Ito J, Zahradnik J, Fujita S, Kosugi Y, Schreiber G, et al. Enhanced transmissibility, infectivity, and immune resistance of the SARS-CoV-2 omicron XBB.1.5 variant. Lancet Infect Dis. 2023 Jan 31:S1473-3099(23)00051-8. doi: 10.1016/S1473-3099(23)00051-8.

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Footnote 10

Qu P, Faraone JN, Evans JP, Zheng Y, Carlin C, Anghelina M, et al. Extraordinary Evasion of Neutralizing Antibody Response by Omicron XBB.1.5, CH.1.1 and CA.3.1 Variants. medRxiv. 2023 Jan 17. doi:

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Footnote 11

Surveillance and Epidemiology Division, Centre for Immunization and Respiratory Infectious Diseases, Infectious Disease Prevention and Control Branch. Data cut-off Dec 18, 2022. Ottawa (ON): Public Health Agency of Canada; 2022 Dec 18.

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Footnote 12

Seroprevalence in Canada. Data cut-off 2022 Dec 31 [Internet]. Montreal (QC): COVID-19 Immunity Task Force (CITF); 2023 Jan [cited 2023 Feb 20]. Available from:

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Footnote 13

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.

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Footnote 14

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.

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Footnote 15

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.

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Footnote 16

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.

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Footnote 17

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.

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Footnote 18

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.

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Footnote 19

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 20

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.

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Footnote 21

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.

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Footnote 22

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.

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Footnote 23

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:

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Footnote 24

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.

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Footnote 25

Bar-On YM, Goldberg Y, Mandel M, Bodenheimer O, Amir O, Freedman L, et al. Protection by a Fourth Dose of BNT162b2 against Omicron in Israel. N Engl J Med. 2022 May 5;386(18):1712,1720. doi: 10.1056/NEJMoa2201570.

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Footnote 26

Gazit S, Saciuk Y, Perez G, Peretz A, Pitzer VE, Patalon T. Short term, relative effectiveness of four doses versus three doses of BNT162b2 vaccine in people aged 60 years and older in Israel: retrospective, test negative, case-control study. BMJ. 2022 May 24;377:e071113. doi: 10.1136/bmj-2022-071113.

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Footnote 27

Grewal R, Nguyen L, Buchan SA, Wilson SE, Costa AP, Kwong JC. Effectiveness and Duration of Protection of a Fourth Dose of COVID-19 mRNA Vaccine among Long-Term Care Residents in Ontario, Canada. medRxiv. 2022 Sep 01.

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Footnote 28

Tseng HF, Ackerson BK, Bruxvoort KJ, Sy LS, Tubert JE, Lee GS, et al. Effectiveness of mRNA-1273 vaccination against SARS-CoV-2 omicron subvariants BA.1, BA.2, BA.2.12.1, BA.4, and BA.5. Nat Commun. 2023 Jan 12;14(1):189. doi: 10.1038/s41467-023-35815-7.

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Footnote 29

Tartof SY, Slezak JM, Puzniak L, Hong V, Frankland TB, Ackerson BK, et al. BNT162b2 vaccine effectiveness against SARS-CoV-2 omicron BA.4 and BA.5. Lancet Infect Dis. 2022 Dec;22(12):1663,1665. doi: 10.1016/S1473-3099(22)00692-2.

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Footnote 30

Barda N, Canetti M, Gilboa M, Indenboim V, Asraf K, Weiss-Ottolenghi Y, et al. Comparing immunogenicity and efficacy of two different mRNA-based COVID-19 vaccines as a fourth dose; six-month follow-up, Israel, 27 December 2021 to 24 July 2022. Euro Surveill. 2022 Sep;27(39):2200701. doi: 10.2807/1560-7917.ES.2022.27.39.2200701.

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Footnote 31

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.

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Footnote 32

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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Footnote 33

Lin D, Xu Y, Gu Y, Zeng D, Wheeler B, Young H, et al. Effectiveness of Bivalent Boosters against Severe Omicron Infection. N Engl J Med. 2023 Jan 25. doi: 10.1056/NEJMc2215471.

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Footnote 34

Lin D, Xu Y, Gu Y, Zeng D, Wheeler B, Young H, et al. Effectiveness of Vaccination and Previous Infection Against Omicron Infection and Severe Outcomes in Children Under 12 Years of Age. medRxiv. 2023 Jan 19.

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Footnote 35

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 36

Andersson NW, Thiesson EM, Baum U, Pihlström N, Starrfelt J, Faksová K, et al. Comparative effectiveness of the bivalent BA.4-5 and BA.1 mRNA-booster vaccines in the Nordic countries. medRxiv. 2023 Jan 19.

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Footnote 37

Lee IT, Cosgrove CA, Moore P, Bethune C, Nally R, Bula M, et al. A Randomized Trial Comparing Omicron-Containing Boosters with the Original Covid-19 Vaccine mRNA-1273. medRxiv. 2023 Jan 24.

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Footnote 38

Link-Gelles R, Ciesla AA, Roper LE, Scobie HM, Ali AR, Miller JD, et al. Early Estimates of Bivalent mRNA Booster Dose Vaccine Effectiveness in Preventing Symptomatic SARS-CoV-2 Infection Attributable to Omicron BA.5- and XBB/XBB.1.5-Related Sublineages Among Immunocompetent Adults - Increasing Community Access to Testing Program, United States, December 2022-January 2023. MMWR Morb Mortal Wkly Rep. 2023 Feb 3;72(5):119,124. doi: 10.15585/mmwr.mm7205e1.

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Footnote 39

Ischaemic stroke following mRNA bivalent COVID-19 vaccination Canada December 1, 2020 - January 6, 2023. [Unpublished]. Ottawa (ON): Public Health Agency of Canada (PHAC); 2023 Jan 18.

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Footnote 40

Lavery I. No 'elevated risk' of stroke from Pfizer's bivalent COVID shot, Health Canada says [Internet]. Global News; 2023 Jan 29 [cited 2023 Feb 02]. Available from:

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Footnote 41

Public Health Agency of Canada. Reported side effects following COVID-19 vaccination in Canada. Data cut-off Feb 3, 2023 [Internet]. Ottawa (ON): Health Canada; 2023 Feb 17 [cited 2023 Feb 20]. Available from:

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Footnote 42

Ontario Agency for Health Protection and Promotion (Public Health Ontario). Adverse events following immunization (AEFIs) for COVID-19 in Ontario: December 13, 2020 to January 29, 2023. Data cut-off Jan 29, 2023 [Internet]. Toronto (ON): King's Printer for Ontario; 2023 Feb 03 [cited 2023 Feb 20]. Available from:

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Footnote 43

Hause AM, Marquez P, Zhang B, Su JR, Myers TR, Gee J, et al. Safety Monitoring of Bivalent COVID-19 mRNA Vaccine Booster Doses Among Children Aged 5-11 Years - United States, October 12-January 1, 2023. MMWR Morb Mortal Wkly Rep. 2023 Jan 13;72(2):39,43. doi: 10.15585/mmwr.mm7202a5.

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Footnote 44

Hause AM, Marquez P, Zhang B, Myers TR, Gee J, Su JR, et al. Safety Monitoring of Bivalent COVID-19 mRNA Vaccine Booster Doses Among Persons Aged ≥12 Years - United States, August 31-October 23, 2022. MMWR Morb Mortal Wkly Rep. 2022 Nov 4;71(44):1401,1406. doi: 10.15585/mmwr.mm7144a3.

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Footnote 45

Andersson NW, Thiesson EM, Vinsløv Hansen J, Hviid A. Safety of bivalent omicron-containing mRNA-booster vaccines: a nationwide cohort study. medRxiv. 2023 Jan 22.

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Footnote 46

Shimabukuro T, Klein, N. COVID-19 mRNA bivalent booster vaccine safety [slides presented at Vaccines and Related Biological Products Advisory Committee (VRBPAC) meeting January 26, 2023] [Internet]. Silver Spring (MD): Food and Drug Administration (FDA); 2023 Jan 26 [cited 2023 Feb 02]. Available from:

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Footnote 47

CDC & FDA Identify Preliminary COVID-19 Vaccine Safety Signal for Persons Aged 65 Years and Older [Internet]. Atlanta (GA): Centers for Disease Control and Prevention (CDC); 2023 Jan 13 [cited 2023 Feb 02]. Available from:

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Footnote 48

Forshee R. Update on Original COVID-19 Vaccine and COVID-19 Vaccine, Bivalent Effectiveness and Safety [slides presented at Vaccines and Related Biological Products Advisory Committee (VRBPAC) meeting January 26, 2023] [Internet]. Silver Spring (MD): Food and Drug Administration (FDA); 2023 Jan 26 [cited 2023 Feb 02]. Available from:

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Footnote 49

Carazo S, Skowronski DM, Brisson M, Sauvageau C, Brousseau N, Fafard J, et al. Prior infection- and/or vaccine-induced protection against Omicron BA.1, BA.2 and BA.4/BA.5-related hospitalisations in older adults: a test-negative case-control study in Quebec, Canada. medRxiv. 2022 Dec 27.

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Footnote 50

Kwong J. Personal communication. 2023 Feb 02.

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Footnote 51

Bobrovitz N, Ware H, Ma X, Li Z, Hosseini R, Cao C, et al. Protective effectiveness of previous SARS-CoV-2 infection and hybrid immunity against the omicron variant and severe disease: a systematic review and meta-regression. Lancet Infect Dis. 2023 Jan 18:S1473-3099(22)00801-5. doi: 10.1016/S1473-3099(22)00801-5.

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