Guidance on an additional dose of COVID-19 vaccines in the spring for individuals at high risk of severe illness due to COVID-19

Download in PDF format
(619 KB, 13 pages)

Organization: Public Health Agency of Canada

Date published: 2024-01-12
Cat.: HP5-176/1-2024E-PDF
ISBN: 978-0-660-69265-4
Pub.: 230641

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 July 11, 2023, NACI provided guidance of the use COVID- 19 vaccines in the fall of 2023, with an addendum later published on September 12, 2023. The advice noted that recommendations on the timing of subsequent doses would be provided, if warranted, as the seasonality of SARS-CoV-2 has not been established and the need for routine programs is still unclear. NACI has previously recommended a vaccine program during the fall/winter and spring periods based on an assessment of the need for and potential benefit of additional doses in certain populations, with the spring program being a smaller and more targeted program for individuals at higher risk for severe illness due to COVID-19.

With provinces and territories having resumed other public health programs and activities, NACI guidance is being provided in advance to facilitate planning for a possible spring program.

NACI's recommendations continue to align with the goals of the Canadian COVID-19 Pandemic Response (February 14, 2022):


On October 17 and 31, 2023, the NACI COVID-19 Working Group (WG) reviewed the available information on SARS-CoV-2 epidemiology and seroprevalence, vaccine effectiveness (VE) of bivalent vaccines, including vaccine duration of protection, and the impact of hybrid immunity. Preliminary cost-effectiveness estimates for a spring 2024 campaign were also reviewed.

On November 15, 2023, NACI reviewed the evidence presented to the COVID-19 WG, along with feedback from provinces and territories on their experience with the spring 2023 COVID-19 vaccine program. NACI reached consensus on proposed recommendations, and approved the Statement on December 11, 2023. An early briefing on the recommendations was provided by NACI to provinces and territories on November 23, 2023 and November 30, 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 in the Canadian Immunization Guide (CIG).

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

Overview of evidence

Information available as of November 15, 2023 is summarized below.


* Includes all descendant lineages, unless otherwise specified.

Vaccine protection and hybrid immunity


Ethics, equity, feasibility, and acceptability (EEFA)


Please see Table 1 for an explanation of strong versus discretionary NACI recommendations.

Starting in the spring of 2024, NACI recommends that the following individuals who are at increased risk of severe illness from COVID-19 may receive an additional dose of XBB.1.5 COVID-19 vaccine:

(Discretionary NACI recommendation)


NACI will continue to monitor the evidence, including SARS-CoV-2 epidemiology, VE of XBB.1.5 vaccines and duration of vaccine protection, particularly with regard to severe outcomes, to provide recommendations on the timing of subsequent doses if warranted.

Table 1. Strength of NACI recommendations

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"

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.

Table 2. Factors supporting a COVID-19 vaccine program in the spring of 2024 and current unknowns

Table 2. Factors supporting a COVID-19 vaccine program in the spring of 2024 and current unknowns
Key considerations Factors supporting a spring 2024 COVID-19 vaccine program Current unknowns
COVID-19 epidemiology
  • Recently circulating variants continue to be antigenically related to the XBB* sublineage
  • Older adults continue to be at higher risk for severe illness due to COVID-19
  • Circulating strains and extent for SARS-CoV-2 circulation in the spring and summer of 2024
Population level cumulative immunity and vaccine coverage
  • Some individuals do not have hybrid immunity (i.e. have never been infected) and rely on vaccine-induced immunity (30 to 40% of individuals 65 years of age and older may not have been infected with SARS-CoV-2)
  • Uptake of the XBB.1.5 COVID-19 vaccine during the fall/winter of 2023 to 2024
Vaccine characteristics in different groups against circulating strains
  • Even in the context of hybrid immunity, protection against infection and severe disease from vaccines and/or prior infection wanes over time, although protection is more sustained against severe COVID-19 illness than against SARS-CoV-2 infection
  • Vaccine effectiveness and duration of protection of the XBB.1.5 COVID-19 vaccine

Research priorities


This statement was prepared by: E Wong, B Warshawsky, R Krishnan, N Islam, K Young, M Tunis, R Harrison, S Wilson, and S Deeks, on behalf of NACI.

NACI gratefully acknowledges the contribution of: J Daniel, C Mauviel, SH Lim, B Lowe, P Luth, 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, J Regan, and M Wallace.

PHAC Participants: N Islam, C Jensen, R Krishnan, SH Lim, R Neves Miranda, M Salvadori, A Tuite, MC Tunis, B Warshawsky, E Wong, R Ximenes, K Young, 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 Apr 19;28:58.

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.

Return to footnote 2 referrer

Footnote 3

Public Health Agency of Canada (PHAC). COVID-19 daily epidemiology update: Testing and variants. Data cut-off 2023 Oct 22 [Internet]. Ottawa, ON: Government of Canada; 2023 Dec 12 [cited Dec 12, 2023]. Available from:

Return to footnote 3 referrer

Footnote 4

COVID-19 Immunity Task Force (CITF). Seroprevalence in Canada. Data cut-off 2023 Sep 30 [Internet]. Montreal (QC): COVID-19 Immunity Task Force (CITF): COVID-19 Immunity Task Force; 2023 Sep 30 [cited 2023 Dec 07]. Available from:

Return to footnote 4 referrer

Footnote 5

Skowronski DM, Kaweski SE, Irvine MA, Chuang ESY, Kim S, Sabaiduc S, et al. Risk of hospital admission and death from first-ever SARS-CoV-2 infection by age group during the Delta and Omicron periods in British Columbia, Canada. CMAJ. 2023 -10-30;195(42):E1427-39.

Return to footnote 5 referrer

Footnote 6

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 6 referrer

Footnote 7

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 7 referrer

Footnote 8

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 8 referrer

Footnote 9

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 9 referrer

Footnote 10

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 10 referrer

Footnote 11

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 11 referrer

Footnote 12

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 12 referrer

Footnote 13

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 13 referrer

Footnote 14

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 14 referrer

Footnote 15

Carazo S, Skowronski DM, Brisson PM, Sauvageau C, Brousseau N, Fafard J, et al. Effectiveness of previous infection-induced and vaccine-induced protection against hospitalisation due to omicron BA subvariants in older adults: a test-negative, case-control study in Quebec, Canada. The Lancet Health Longevity. 2023 Aug 2;4(8):e409-20.

Return to footnote 15 referrer

Footnote 16

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.

Return to footnote 16 referrer

Footnote 17

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 17 referrer

Footnote 18

Link-Gelles R. Updates to COVID-19 Vaccine Effectiveness (VE) in the U.S. . [slides presented at Advisory Committee on Immunization Practices (ACIP) meeting Sept 12, 2023] [Internet]. Atlanta (GA): CDC; 2023 Sep 12 Available from:

Return to footnote 18 referrer

Footnote 19

Public Health Agency of Canada (PHAC) Vaccine Coverage Team. Personal Communication. Table 1. % of people who received a dose between April 1 and June 18, 2023. 2023 Oct 12.

Return to footnote 19 referrer

Page details

Date modified: