Guidance on the use of COVID-19 vaccines in the fall of 2023

Download in PDF format
(440 KB, 20 pages)

Organization: Health Canada or Public Health Agency of Canada

Date published: July 11, 2023

Cat.: HP5-159/1-2023E-PDF

ISBN: 978-0-660-49305-3

Pub.: 230214

 Publication date: July 11, 2023

On this page


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, the National Advisory Committee on Immunization (NACI) published Guidance on COVID-19 vaccine booster doses: Initial considerations for 2023, followed by 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 on March 3, 2023.

Since then, the World Health Organization (WHO) has determined that COVID-19 is an established and ongoing health issue and no longer constitutes a public health emergency of international concernFootnote 1. Transition to the long-term management of the COVID-19 pandemic is now needed, but there continue to be uncertainties such as the ongoing epidemiology of COVID-19, duration of protection from current COVID-19 booster doses and previous infection, and vaccine effectiveness (VE) of future vaccines.

On May 18, 2023, the WHO Technical Advisory Group on COVID-19 Vaccine Composition (TAG-CO-VAC) released recommendations for updates to COVID-19 vaccine antigen compositionFootnote 2. An approach recommended by TAG-CO-VAC is a monovalent XBB.1 descendent lineage, such as XBB.1.5 or alternatively XBB.1.16. The International Coalition of Medicines Regulatory Authorities (ICMRA), European Centre for Disease Prevention (ECDC), the European Medicines Agency (EMA), and the US Food and Drug Administration Vaccines and Related Biological Products Advisory Committee (FDA VRBPAC) have also released decisions supporting XBB as a candidate for the COVID-19 vaccine composition update. Manufacturers have indicated that new COVID-19 vaccine formulations are in development and products are forthcoming.

Although seasonality of SARS-CoV-2 has not been established, other respiratory viruses such as influenza and respiratory syncytial virus (RSV) typically increase in the fall and winter months. To help reduce the impact of COVID-19 on the health system while other respiratory viruses are circulating and with the expected availability of a new COVID-19 vaccine formulation, NACI is providing guidance on the use of COVID-19 vaccines to inform planning for a vaccination program starting in fall 2023.


Following preliminary discussions on April 28, 2023, the NACI COVID-19 Working Group and full NACI membership reviewed, on May 23, 2023 and June 6, 2023 respectively, the available evidence on epidemiology, vaccine protection, hybrid immunity, safety, and concurrent administration of COVID-19 vaccine with the seasonal influenza vaccine. Preliminary modelling data were also considered, as well as equity, feasibility and acceptability considerations for a fall 2023 COVID-19 vaccination program. NACI approved these recommendations on June 26, 2023.

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

Further information on NACI’s process and procedures is available elsewhereFootnote 3Footnote 4.

Overview of evidence

Available scientific literature (published or pre-print) as of May 19, 2023 is summarized below.


Vaccine protection

Duration of vaccine protection of Omicron-containing bivalent mRNA vaccines

VE in individuals with hybrid immunity

Vaccination of individuals who are pregnant

Post-COVID-19 condition

Safety of Omicron-containing bivalent mRNA COVID-19 vaccines

Concurrent administration with influenza vaccination

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 COVID-19 vaccination for those who have not been immunized, as follows:

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

Regarding the product offered, when mRNA vaccines are used for the primary series, the bivalent Omicron-containing vaccines can be used for anyone 6 months of age and older. More information is available in the NACI interim guidance on the use of bivalent Omicron-containing COVID-19 vaccines for primary series.

For booster doses, previously NACI has recommended that 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, along with additional specific population recommendations in the fall of 2022 and spring of 2023.  

Additional details including those pertaining to vaccine schedule (e.g., number of doses, interval between doses) and alternative vaccine products, are available in the COVID-19 vaccine chapter of the Canadian Immunization Guide and NACI statements and publications.

  1. Beginning in the fall of 2023 for those previously vaccinated against COVID-19, NACI recommends a dose of the new formulation of COVID-19 vaccine for individuals in the authorized age group if it has been at least 6 months from the previous COVID-19 vaccine dose or known SARS-CoV-2 infection (whichever is later).

    Immunization is particularly important for those at increased risk of COVID-19 infection or severe disease, for example:

    • Adults 65 years of age or older
    • Residents of long-term care homes and other congregate living settings
    • Individuals with underlying medical conditions that place them at higher risk of severe COVID-19
    • Individuals who are pregnant
    • Individuals in or from First Nations, Métis and Inuit communities*
    • Members of racialized and other equity-deserving communities
    • People who provide essential community services

(Strong NACI Recommendation)

* Autonomous decisions should be made by Indigenous Peoples with the support of healthcare and public health partners in accordance with the United Nations Declaration on the Rights of Indigenous Peoples.

Rationale and additional considerations:

NACI will review available information on the new vaccine formulations expected for the fall of 2023 and update recommendations as needed. NACI will continue to monitor the evidence, including SARS-CoV-2 epidemiology and duration of vaccine protection, particularly with regard to severe outcomes, to provide recommendations on the timing of subsequent booster doses if warranted.

Research priorities

  1. Continuous monitoring of data on the safety, immunogenicity, efficacy, and effectiveness of COVID-19 vaccines, including with the new formulation, 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 infection such as PCC.
  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, 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 in children, including risk factors for severe outcomes and long-term consequences of infection with SARS-CoV-2.
  5. Continuous monitoring of COVID-19 epidemiology and VE in special populations at high risk of severe outcomes or long-term consequences of infection with SARS-CoV-2.
  6. Further evaluations on the safety, immunogenicity, and effectiveness on the concurrent administration of COVID-19 vaccines with other vaccines across different age groups, including concurrent administration with high dose or adjuvanted influenza vaccine.
  7. 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.
  8. 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.
  9. Continuous monitoring of epidemiology, SARS-CoV-2 variants, and seasonal trends to inform future programs.

Table 1. Strength of NACI recommendations

Strength of NACI recommendation
based on factors not isolated to strength of evidence
(e.g., public health need)




"should/should not be offered"

"may/may not be offered"


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.


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, 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, J Zafack, SH Lim, K Young, 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), 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), M Su (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, M Baca-Estrada, Y-G Bui, H Decaluwe, P De Wals, V Dubey, S Hosseini-Moghaddam, M Miller, D Moore, S Oliver, and E Twentyman.

PHAC Participants: E Abrams, P Doyon-Plourde, N Forbes, M Hersi, N Islam, SJ Ismail, C Jensen, R Krishnan, SH Lim, R Neves Miranda, J Montroy, R Pless, M Salvadori, E Tice, A Tuite, MC Tunis, B Warshawsky, E Wong, R Ximenes, K Young, and J Zafack.


Footnote 1

Statement on the fifteenth meeting of the IHR (2005) Emergency Committee on the COVID-19 pandemic [Internet]. Geneva (CH): World Health Organization; 2023 May 05 [cited 2023 May 25]. Available from:

Return to footnote 1

Footnote 2

Statement on the antigen composition of COVID-19 vaccines [Internet]. Geneva (CH): World Health Organization; 2023 May 18 [cited 2023 May 29]. Available from:

Return to footnote 2

Footnote 3

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 3

Footnote 4

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 4

Footnote 5

Public Health Agency of Canada. COVID-19 epidemiology update: Testing and variants. Data cut-off 2023 May 19 [Internet]. Ottawa (ON): Government of Canada; 2023 May 19 [cited 2023 May 25]. Available from:

Return to footnote 5

Footnote 6

Seroprevalence in Canada. Data cut-off 2023 March 31 [Internet]. Montreal (QC): COVID-19 Immunity Task Force (CITF); 2023 Mar 31 [cited 2023 May 22]. Available from:

Return to footnote 6

Footnote 7

COVID-19 epidemiology update: Current situation. Data cut-off May 17, 2023 [Internet]. Ottawa (ON): Government of Canada; 2023 May 17 [cited 2023 May 25]. Available from:

Return to footnote 7

Footnote 8

Public Health Agency of Canada. Surveillance and Epidemiology Division, Centre for Immunization and Respiratory Infectious Diseases, Infectious Disease Prevention and Control Branch. Data cut-off 2023 May 26. Ottawa (ON): PHAC; 2023 May 26.

Return to footnote 8

Footnote 9

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 May;23(5).

Return to footnote 9

Footnote 10

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.

Return to footnote 10

Footnote 11

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.

Return to footnote 11

Footnote 12

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.

Return to footnote 12

Footnote 13

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.

Return to footnote 13

Footnote 14

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):1770-82.

Return to footnote 14

Footnote 15

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.

Return to footnote 15

Footnote 16

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.

Return to footnote 16

Footnote 17

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.

Return to footnote 17

Footnote 18

Huiberts AJ, Gier Bd, Hoeve CE, Melker HEd, Hahné SJ, Hartog Gd, et al. Effectiveness of bivalent mRNA booster vaccination against SARS-CoV-2 Omicron infection, the Netherlands, September to December 2022. Eurosurveillance. 2023 Feb 16;28(7):2300087.

Return to footnote 18

Footnote 19

Fabiani M, Mateo-Urdiales A, Sacco C, Fotakis EA, Rota MC, Petrone D, et al. Protection against severe COVID-19 after second booster dose of adapted bivalent (original/Omicron BA.4-5) mRNA vaccine in persons ≥ 60 years, by time since infection, Italy, 12 September to 11 December 2022. Eurosurveillance. 2023 Feb 23;28(8):2300105.

Return to footnote 19

Footnote 20

RESPIPLUS. Personal Communication. RESPIPLUS Review. 2023 May 02.

Return to footnote 20

Footnote 21

Kulkarni D, Ismail NF, Zhu F, Wang X, del Carmen Morales G, Allen KE, et al. Epidemiology and Clinical Features of SARS-CoV-2 Infection in Children and Adolescents in the Pre-Omicron Era: A Global Systematic Review and Meta-Analysis. SSRN Prepub. 2023 Mar 26.

Return to footnote 21

Footnote 22

Link-Gelles R. COVID-19 vaccine effectiveness updates [slides presented at Advisory Committee on Immunization Practices (ACIP) meeting April 19, 2023] [Internet]. Atlanta (GA): Centers for Disease Control and Prevention (CDC); 2023 Apr 19 [cited 2023 May 30]. Available from:

Return to footnote 22

Footnote 23

Lin D, Xu Y, Gu Y, Zeng D, Sunny SK, Moore Z. Durability of Bivalent Boosters against Omicron Subvariants. The New England journal of medicine. 2023 May 11;388(19):1818-20.

Return to footnote 23

Footnote 24

Poukka E, Nohynek H, Goebeler S, Leino T, Baum U. Bivalent booster effectiveness against severe COVID-19 outcomes in Finland, September 2022 – March 2023. medRxiv. 2023 May 08.

Return to footnote 24

Footnote 25

Grewal, Buchan, Nguyen, Nasreen, Austin, Brown, et al. Effectiveness of mRNA COVID-19 monovalent and bivalent vaccine booster doses against Omicron severe outcomes among adults aged ≥50 years in Ontario, Canada. medRxiv. 2023 Apr 11.

Return to footnote 25

Footnote 26

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.

Return to footnote 26

Footnote 27

Jang EJ, Choe YJ, Kim RK, Park Y. BNT162b2 Vaccine Effectiveness Against the SARS-CoV-2 Omicron Variant in Children Aged 5 to 11 Years. JAMA Pediatrics. 2023 Mar 01;177(3):319-20.

Return to footnote 27

Footnote 28

Sacco C, Del Manso M, Mateo-Urdiales A, Rota MC, Petrone D, Riccardo F, et al. Effectiveness of BNT162b2 vaccine against SARS-CoV-2 infection and severe COVID-19 in children aged 5–11 years in Italy: a retrospective analysis of January–April, 2022. The Lancet (British edition). 2022 Jul 09;400(10346):97-103.

Return to footnote 28

Footnote 29

Tan SHX, Cook AR, Heng D, Ong B, Lye DC, Tan KB. Effectiveness of BNT162b2 Vaccine against Omicron in Children 5 to 11 Years of Age. New England Journal of Medicine. 2022 Aug 11;387(6):525-32.

Return to footnote 29

Footnote 30

Cocchio S, Zabeo F, Tremolada G, Facchin G, Venturato G, Marcon T, et al. COVID-19 Vaccine Effectiveness against Omicron Variant among Underage Subjects: The Veneto Region’s Experience. Vaccines (Basel). 2022 Aug 20;10(8):1362.

Return to footnote 30

Footnote 31

Piché-Renaud P, Swayze S, Buchan SA, Wilson SE, Austin PC, Morris SK, et al. COVID-19 Vaccine Effectiveness Against Omicron Infection and Hospitalization. Pediatrics (Evanston). 2023 Mar 03;151(4):e2022059513.

Return to footnote 31

Footnote 32

Lin D, Gu Y, Xu Y, Zeng D, Wheeler B, Young H, et al. Effects of Vaccination and Previous Infection on Omicron Infections in Children. New England Journal of Medicine. 2022 Sep 22;387(12):1141-3.

Return to footnote 32

Footnote 33

Khan FL, Nguyen JL, Singh TG, Puzniak LA, Wiemken TL, Schrecker JP, et al. Estimated BNT162b2 Vaccine Effectiveness Against Infection With Delta and Omicron Variants Among US Children 5 to 11 Years of Age. JAMA Network Open. 2022 Dec 14;5(12):e2246915.

Return to footnote 33

Footnote 34

Fleming-Dutra KE, Britton A, Shang N, Derado G, Link-Gelles R, Accorsi EK, et al. Association of Prior BNT162b2 COVID-19 Vaccination With Symptomatic SARS-CoV-2 Infection in Children and Adolescents During Omicron Predominance. JAMA : the journal of the American Medical Association. 2022 Jun 14;327(22):2210-9.

Return to footnote 34

Footnote 35

Florentino PTV, Millington T, Cerqueira-Silva T, Robertson C, de Araújo Oliveira V, Júnior JBS, et al. Vaccine effectiveness of two-dose BNT162b2 against symptomatic and severe COVID-19 among adolescents in Brazil and Scotland over time: a test-negative case-control study. Lancet Infect Dis. 2022 -Nov;22(11):1577-86.

Return to footnote 35

Footnote 36

Ionescu IG, Skowronski DM, Sauvageau C, Chuang E, Ouakki M, Kim S, et al. BNT162b2 effectiveness against Delta & Omicron variants in teens by dosing interval and duration. medRxiv. 2022 Jul 13.

Return to footnote 36

Footnote 37

Buchan SA, Nguyen L, Wilson SE, Kitchen SA, Kwong JC. Vaccine Effectiveness of BNT162b2 Against Delta and Omicron Variants in Adolescents. Pediatrics. 2022 Jun 16.

Return to footnote 37

Footnote 38

Fleming-Dutra KE, Ciesla AA, Roper LE, Smith ZR, Miller JD, Accorsi EK, et al. Preliminary Estimates of Effectiveness of Monovalent mRNA Vaccines in Preventing Symptomatic SARS-CoV-2 Infection Among Children Aged 3-5 Years - Increasing Community Access to Testing Program, United States, July 2022-February 2023. MMWR Morb Mortal Wkly Rep. 2023 Feb 17;72(7):177-82.

Return to footnote 38

Footnote 39

Yan VKC, Cheng FWT, Chui CSL, Lai FTT, Wong CKH, Li X, et al. Effectiveness of BNT162b2 and CoronaVac vaccines in preventing SARS-CoV-2 Omicron infections, hospitalizations, and severe complications in the pediatric population in Hong Kong: a case-control study. Emerging Microbes & Infections. 2023 Mar 15;12(1):2185455.

Return to footnote 39

Footnote 40

Jorgensen SC, Hernandez A, Fell D, Austin PC, D’Souza R, Guttmann A, et al. Effectiveness of Maternal mRNA COVID-19 Vaccination During Pregnancy Against Delta and Omicron SARS-CoV-2 Infection and Hospitalization in Infants: A Test-Negative Design Study. SSRN Electronic Journal. 2022 Nov 08.

Return to footnote 40

Footnote 41

Zerbo O, Ray GT, Fireman B, Layefsky E, Goddard K, Lewis E, et al. Maternal SARS-CoV-2 vaccination and infant protection against SARS-CoV-2 during the first six months of life. Nat Commun. 2023 Feb 28;14(1):1-8.

Return to footnote 41

Footnote 42

Lipschuetz M, Guedalia J, Cohen SM, Sompolinsky Y, Shefer G, Melul E, et al. Maternal third dose of BNT162b2 mRNA vaccine and risk of infant COVID-19 hospitalization. Nat Med. 2023 Mar 23;29(5):1155-63.

Return to footnote 42

Footnote 43

Jorgensen SCJ, Hernandez A, Fell DB, Austin PC, D’Souza R, Guttmann A, et al. Estimated Effectiveness of Postpartum Maternal Messenger RNA COVID-19 Vaccination Against Delta and Omicron SARS-CoV-2 Infection and Hospitalization in Infants Younger Than 6 Months. JAMA Pediatrics. 2023 Apr 01;177(4):427-30.

Return to footnote 43

Footnote 44

Antonelli M, Pujol JC, Spector TD, Ourselin S, Steves CJ. Risk of long COVID associated with delta versus omicron variants of SARS-CoV-2. The Lancet (British edition). 2022 Jun 18;399(10343):2263-4.

Return to footnote 44

Footnote 45

Spiliopoulos L, Sørensen AIV, Bager P, Nielsen NM, Hansen JV, Koch A, et al. Post-acute symptoms four months after SARS-CoV-2 infection during the Omicron period: a nationwide Danish questionnaire study. medRxiv. 2022 Oct 28.

Return to footnote 45

Footnote 46

Kahlert CR, Strahm C, Güsewell S, Cusini A, Brucher A, Goppel S, et al. Association of viral variant and vaccination status with the occurrence of symptoms compatible with post-acute sequelae after primary SARS-CoV-2 infection. medRxiv. 2022 Oct 22.

Return to footnote 46

Footnote 47

Quinn KL, Katz GM, Bobos P, Sander B, McNaughton CD, Cheung AM, et al. Understanding the Post COVID-19 Condition (Long COVID) in Adults and the Expected Burden for Ontario. Science Briefs of the Ontario COVID-19 Science Advisory Table. 2022 Sep 06;3(65).

Return to footnote 47

Footnote 48

Coronavirus disease (COVID-19): Post COVID-19 condition [Internet]. Geneva (CH): World Health Organization; 2023 Mar 28 [cited 2023 Jun 07]. Available from:

Return to footnote 48

Footnote 49

Watanabe A, Iwagami M, Yasuhara J, Takagi H, Kuno T. Protective effect of COVID-19 vaccination against long COVID syndrome: A systematic review and meta-analysis. Vaccine. 2023 Mar 10;41(11):1783-90.

Return to footnote 49

Footnote 50

Azzolini E, Levi R, Sarti R, Pozzi C, Mollura M, Mantovani A, et al. Association Between BNT162b2 Vaccination and Long COVID After Infections Not Requiring Hospitalization in Health Care Workers. JAMA : the journal of the American Medical Association. 2022 Jul 01;328(7):676-8.

Return to footnote 50

Footnote 51

Ballouz T, Menges D, Kaufmann M, Amati R, Frei A, Wyl Vv, et al. Post COVID-19 condition after Wildtype, Delta, and Omicron SARS-CoV-2 infection and prior vaccination: Pooled analysis of two population-based cohorts. PLOS ONE. 2022 Feb 22;18(2):e0281429.

Return to footnote 51

Footnote 52

Shimabukuro T. mRNA COVID-19 bivalent booster vaccine
safety update [slides presented at Advisory Committee on Immunization Practices (ACIP) meeting April 19, 2023] [Internet]. Atlanta (GA): Centers for Disease Control and Prevention; 2023 Apr 19 [cited 2023 May 25]. Available from:

Return to footnote 52

Footnote 53

Vaccine Safety Surveillance Division. Personal communication. CAEFISS update. 2023 May 18.

Return to footnote 53

Footnote 54

Andrews N, Stowe J, Miller E, Ramsay M. BA.1 Bivalent COVID-19 Vaccine Use and Stroke in England. JAMA. 2023 Jun 15:e2310123.

Return to footnote 54

Footnote 55

Janssen C, Mosnier A, Gavazzi G, Combadière B, Crépey P, Gaillat J, et al. Coadministration of seasonal influenza and COVID-19 vaccines: A systematic review of clinical studies. Hum Vaccin Immunother. 2022 Nov 30;18(6):2131166.

Return to footnote 55

Footnote 56

Wagenhäuser I, Reusch J, Gabel A, Höhn A, Lâm T, Almanzar G, et al. Immunogenicity and safety of coadministration of COVID-19 and influenza vaccination. European Respiratory Journal. 2023 Jan 06;61(1):2201390.

Return to footnote 56

Footnote 57

Kim A, Kim S, Song J, Hwang S, Nam E, Kwon KT. Adverse Reactions after BNT162b2 Messenger RNA Vaccination for Coronavirus Disease 2019 in Healthcare Workers Compared with Influenza Vaccination. Vaccines (Basel). 2023 Feb 05;11(2):363.

Return to footnote 57

Footnote 58

Radner H, Sieghart D, Jorda A, Fedrizzi C, Hasenöhrl T, Zdravkovic A, et al. Reduced immunogenicity of BNT162b2 booster vaccination in combination with a tetravalent influenza vaccination: results of a prospective cohort study in 838 health workers. Clin Microbiol Infect. 2023 May;29(5):635-41.

Return to footnote 58

Footnote 59

Toback S, Galiza E, Cosgrove C, Galloway J, Goodman AL, Swift PA, et al. Safety, immunogenicity, and efficacy of a COVID-19 vaccine (NVX-CoV2373) co-administered with seasonal influenza vaccines: an exploratory substudy of a randomised, observer-blinded, placebo-controlled, phase 3 trial. Lancet Respir Med. 2022 Feb;10(2):167-4.

Return to footnote 59

Footnote 60

Izikson R, Brune D, Bolduc JS, Bourron P, Fournier M, Moore TM, et al. Safety and immunogenicity of a high-dose quadrivalent influenza vaccine administered concomitantly with a third dose of the mRNA-1273 SARS-CoV-2 vaccine in adults aged ≥65 years: a phase 2, randomised, open-label study. Lancet Respir Med. 2022 Apr 01;10(4):392-9.

Return to footnote 60

Footnote 61

Public Health Agency of Canada. Vaccination coverage by age, sex, and province or territory. Data cut-off April 23, 2023 [Internet]. Ottawa (ON): Government of Canada; 2023 Apr 23 [cited 2023 May 30]. Available from:

Return to footnote 61

Footnote 62

Vaccines and Related Biological Products Advisory Committee June 15, 2023 Meeting Announcement [Internet]. Silver Spring (MD): U.S. Food and Drug Administration; 2023 Jun 15 [cited 2023 Jun 16]. Available from:

Return to footnote 62

Page details

Date modified: