NACI Vaccine Statement for 2024–2025

Abstract

Background: The National Advisory Committee on Immunization (NACI) reviews the evolving evidence on influenza immunization and provides annual recommendations regarding the use of seasonal influenza vaccines. The NACI Statement on Seasonal Influenza Vaccine for 2024–2025 updates the NACI recommendations from the previous year.

Objective: To summarize the 2024–2025 NACI seasonal influenza vaccine recommendations and to highlight new and updated information.

Methods: For the development of the Statement on Seasonal Influenza Vaccine for 2024–2025, the NACI Influenza Working Group applied the NACI evidence-based process to assess available evidence and formulate recommendations. These recommendations underwent a thorough evaluation and were approved by NACI based on the available evidence.

Results: Key updates for the 2024–2025 influenza season include updated immunization recommendations reflecting changes in influenza epidemiology and revised guidance for vaccine administration during pregnancy and in older adults.

Conclusion: The National Advisory Committee on Immunization recommends that any age-appropriate quadrivalent or trivalent influenza vaccine should be used for individuals six months of age and older who do not have contraindications or precautions. NACI reaffirms the importance of influenza vaccination with inactivated or recombinant influenza vaccines in pregnancy. Finally, NACI recommends that inactivated high-dose (IIV-HD), inactivated adjuvanted (IIV-Adj) or recombinant influenza vaccine (RIV) should be offered, when available, over other influenza vaccines for adults 65 years of age and older.

Introduction

Each year, Canada experiences seasonal influenza epidemics, primarily during late fall and winter. The severity of these outbreaks fluctuates annually due to factors such as circulating virus types and affected populations ^{Footnote 1}. On average, Canada sees approximately 12,200 influenza-related hospitalizations and 3,500 influenza-related deaths annually ^{Footnote 2Footnote 3}. Vaccination remains the most effective defence against influenza and its complications.

The National Advisory Committee on Immunization (NACI) provides the Public Health Agency of Canada (PHAC) with annual recommendations on the use of authorized seasonal influenza vaccines, reflecting shifts in epidemiology, immunization practices and available products in Canada. The NACI Influenza Working Group leads the annual update of the NACI Statement on Seasonal Influenza Vaccine, involving a thorough review and evaluation of the literature as well as discussion and debate at the scientific and clinical practice levels. On July 25, 2024, PHAC released new guidance from NACI on the use of seasonal influenza vaccines for the 2024–2025 season, which is based on current evidence and expert opinion. This article provides a concise summary of NACI's recommendations and supporting information for the 2024–2025 influenza season, with emphasis on new or updated information since the Statement on Seasonal Influenza Vaccine for 2023–2024. Conclusions from evidence reviews on the use of influenza vaccine during pregnancy and in older adults are also presented. Additionally, the article addresses ongoing research following recent outbreaks of highly pathogenic avian influenza (HPAI) A(H5N1). For detailed information, refer to the new NACI Advisory Committee Statement on Seasonal Influenza Vaccine for 2024–2025 (the Statement) on the PHAC website ^{Footnote 4}.

Methods

In the preparation of the 2024–2025 seasonal influenza vaccine recommendations, NACI's Influenza Working Group identified the need for evidence reviews for new topics, analyzed available evidence and developed updated recommendations using NACI's evidence-based process. Further details regarding the strength of NACI recommendations are available in Table A1 in the Appendix. NACI's peer-reviewed framework and evidence-informed tools (including the Ethics Integrated Filters, Equity Matrix, Feasibility Matrix and Acceptability Matrix) were applied to help ensure that issues related to ethics, equity, feasibility and acceptability are systematically assessed and integrated into NACI guidance ^{Footnote 5}.

The 2024–2025 Statement includes an addendum ^{Footnote 6} with updated guidance on influenza immunization in response to the global absence of B/Yamagata viruses. Recommendations and supporting evidence from 1) Updated Guidance on Influenza Vaccination During Pregnancy ^{Footnote 7} and 2) Supplemental Guidance on Influenza Vaccination in Adults 65 Years of Age and Older ^{Footnote 8}, both published since the 2023–2024 Statement, were also integrated.

For more information on NACI recommendations related to seasonal influenza vaccination, please see the Canadian Immunization Guide chapter on influenza vaccines ^{Footnote 9}, as well as additional statements on the NACI web page.

Results

New or updated information for 2024–2025

Addendum to the 2024–2025 Statement: The 2024–2025 Statement includes an addendum with updated information and guidance on influenza vaccines, reflecting the global absence of B/Yamagata viruses since March 2020. NACI supports transitioning from quadrivalent to trivalent influenza vaccines based on this change in epidemiology, the theoretical risk of reintroduction of B/Yamagata viruses with the continued production and use of quadrivalent vaccines, and World Health Organization (WHO) recommendations and expert consensus. Therefore, NACI has removed its preferential recommendation for quadrivalent vaccines in children, and now, NACI recommends that any age-appropriate quadrivalent or trivalent influenza vaccine should be used for individuals six months of age and older who do not have contraindications or precautions. For the 2024–2025 influenza season in Canada, vaccine availability is anticipated to remain unchanged, with quadrivalent formulations continuing to be supplied for public programs. Adjuvanted inactivated influenza vaccines will remain trivalent and continue to be available in Canada. Please refer to the Addendum to the NACI Statement on Seasonal Influenza Vaccine for 2024–2025 – Transition from Quadrivalent to Trivalent Influenza Vaccines for more information ^{Footnote 6}.

For the 2023–2024 influenza season, NACI reviewed the available evidence and developed updated recommendations for the following topics:

• The use of influenza vaccines during pregnancy: NACI continues to strongly recommend that inactivated or recombinant influenza vaccines be offered during pregnancy, at any gestational age. NACI also continues to include pregnant individuals among those for whom influenza vaccination is particularly important. Finally, NACI reaffirms its recommendation that influenza vaccination may be given at the same time as, or at any time before or after administration of another vaccine, including the COVID-19 or pertussis vaccine.

  For complete details of this review, rationale, relevant considerations and additional information supporting this recommendation, refer to the Updated Guidance on Influenza Vaccination During Pregnancy ^{Footnote 7}.

• The use of influenza vaccines in older adults: NACI strongly recommends that inactivated high-dose (IIV-HD), inactivated adjuvanted (IIV-Adj) or recombinant influenza vaccine (RIV) should be offered, when available, over other influenza vaccines for adults 65 years of age and older. If a preferred product is not available, any of the available age-appropriate influenza vaccines should be used.

  For complete details of this review, rationale, relevant considerations and additional information supporting this recommendation, refer to the Supplemental Guidance on Influenza Vaccination in Adults 65 Years of Age and Older ^{Footnote 8}.

Seasonal influenza guidance in the context of highly pathogenic avian influenza (HPAI) A(H5N1) outbreaks: Due to recent HPAI A(H5N1) outbreaks in poultry and mammals, including, as of July 2024, multiple cases in the United States of bird-to-human and cow-to-human transmissions, NACI reiterates its recommendation that all individuals six months of age and older should receive a seasonal influenza vaccine. This includes those likely to have significant risk of exposure to influenza A(H5N1) through interactions with birds or mammals (such as poultry, livestock, slaughterhouse and processing plant workers, wildlife officers/researchers and veterinarians). NACI will be conducting an evidence review to determine if there is a need to permanently expand its list of individuals for whom influenza vaccination is particularly important, beyond the current group, to others at high risk of exposure to circulating A(H5N1) viruses.

More information can be found in the Important notice 2: Outbreaks of highly pathogenic avian influenza in Canada and U.S. section of the Seasonal Influenza Vaccine for 2024–2025 on the PHAC website ^{Footnote 4}.

Summary of National Advisory Committee on Immunization recommendations for the use of influenza vaccines for the 2024–2025 influenza season

The National Advisory Committee on Immunization recommends that any age-appropriate quadrivalent or trivalent influenza vaccine should be used for individuals six months of age and older who do not have contraindications or precautions. Vaccination should be offered as a priority to people at high risk of influenza-related complications or hospitalization, people capable of transmitting influenza to those at high risk of complications and others as indicated in List 1:

• Both quadrivalent and trivalent formulations are clinically safe and effective
• Since March 2020, B/Yamagata viruses have not been detected globally, leading to the recommendation to exclude the B/Yamagata component from 2024 to 2025 influenza vaccines, aligning with WHO guidance
• Previously, quadrivalent vaccines were preferred for children due to the presence of both influenza B components, and NACI now has no preference between quadrivalent and trivalent vaccines

List 1: Groups for whom influenza vaccination is particularly important^{Footnote a}

People at high risk of influenza-related complications or hospitalization: All children 6–59 months of age Adults and children with the following chronic health conditionsFootnote b: Cardiac or pulmonary disorders (including bronchopulmonary dysplasia, cystic fibrosis and asthma) Diabetes mellitus and other metabolic diseases Cancer, immune compromising conditions (due to underlying disease, therapy, or both, such as solid organ transplant or hematopoietic stem cell transplant recipients) Renal disease Anemia or hemoglobinopathy Neurologic or neurodevelopmental conditions (includes neuromuscular, neurovascular, neurodegenerative, neurodevelopmental conditions and seizure disorders [and, for children, includes febrile seizures and isolated developmental delay], but excludes migraines and psychiatric conditions without neurological conditions)Footnote c Morbid obesity (defined as BMI of 40 kg/m2 and over) Children six months to 18 years of age undergoing treatment for long periods with acetylsalicylic acid, because of the potential increase of Reye syndrome associated with influenza All individuals who are pregnant All individuals of any age who are residents of nursing homes and other chronic care facilities Adults 65 years of age and older Indigenous Peoples People capable of transmitting influenza to those at high risk: Healthcare and other care providers in facilities and community settings who, through their activities, are capable of transmitting influenza to those at high risk Household contacts, both adults and children, of individuals at high risk, whether or not the individual at high risk has been vaccinated: Household contacts of individuals at high risk Household contacts of infants younger than six months of age, as these infants are at high risk but cannot receive influenza vaccine Members of a household expecting a newborn during the influenza season Those providing regular childcare to children newborn to 59 months of age, whether in or out of the home Those who provide services within closed or relatively closed settings to people at high risk (e.g., crew on a cruise ship) Others: People who provide essential community services People who are in direct contact with poultry infected with avian influenza during culling operations

Footnote a List reproduced from NACI Seasonal Influenza Vaccine Statement for 2024–2025 Footnote 4 Return to footnote a referrer Footnote b Refer to Immunization of Persons with Chronic Diseases Footnote 10 and Immunization of Immunocompromised Persons Footnote 11 in Part 3 of the Canadian Immunization Guide for additional information about vaccination of people with chronic diseases Return to footnote b referrer Footnote c Refer to the NACI Statement on Seasonal Influenza Vaccine for 2018–2019 Footnote 12 for rationale supporting the decision to include persons with neurologic or neurodevelopment conditions among the groups for whom influenza vaccination is particularly important and the Literature Review on Individuals with Neurologic or Neurodevelopment Conditions and Risk of Serious Influenza-Related Complications Footnote 13 for additional details of the evidence reviews that were conducted Return to footnote c referrer

Recommendations on choice of influenza vaccine type for individual and public health program-level decision making by age group

• Children aged six to 23 months can receive IIV-Adj, standard-dose inactivated influenza vaccine (IIV-SD) and mammalian cell culture based inactivated influenza vaccine (IIV-cc).
  • Influvac Tetra (IIV4-SD) is not recommended for those younger than three years due to insufficient evidence.
• Children six to 17 years can receive IIV-SD, IIV-cc and live attenuated influenza vaccine (LAIV).
  • LAIV is suitable for children with stable, non-severe asthma, cystic fibrosis (without immunosuppressive drug treatment) and stable HIV infection (if being treated with antiretroviral therapy and has adequate immune function).
  • LAIV should not be used in children or adolescents with contraindications or precautions, including severe asthma, medically attended wheezing within the past seven days, current receipt of aspirin or aspirin-containing therapy and immune compromising conditions. Stable HIV infection is an exception, provided the child has been on highly active antiretroviral therapy for at least four months with adequate immune function. Live attenuated influenza vaccine should also not be used in pregnancy; IIV-SD or IIV-cc are preferred choices during pregnancy.
  • IIV4-SD is not recommended for those younger than three years due to insufficient evidence.
• Adults 18 to 59 years can receive IIV-SD, IIV-cc, RIV and LAIV; however, inactivated influenza vaccine may provide better protection than LAIV in healthy adults.
  • LAIV is not recommended for adults with any chronic health conditions listed in List 1 (including immune compromising conditions) and healthcare workers. LAIV is also not recommended in pregnancy; IIV-SD, IIV-cc or RIV are preferred choices during pregnancy.
• Adults 60 to 64 years can receive IIV-SD, IIV-cc and RIV.
• Adults 65 years of age and older should preferentially receive IIV-HD, IIV-Adj or RIV, when available, over IIV-SD and IIV-cc. If a preferred product is not available, any age-appropriate influenza vaccine should be used.

For more information, refer to the Addendum to the NACI Statement on Seasonal Influenza Vaccine for 2024–2025 – Transition from Quadrivalent to Trivalent Influenza Vaccines ^{Footnote 6}. The Canadian Immunization Guide Chapter on Influenza Vaccines has also been updated accordingly.

Recommended dose and route of administration of influenza vaccine types by age, are summarized in Table 1.

Conclusion

The National Advisory Committee on Immunization continues to recommend annual influenza vaccination for all individuals aged six months and older (noting product-specific age indications and contraindications). Influenza vaccination is particularly important for people at high risk of influenza-related complications or hospitalization, people capable of transmitting influenza to those at high risk, people who provide essential community services and people in direct contact during culling operations with poultry infected with avian influenza. For the 2024–2025 influenza season, NACI: 1) recommends that any age-appropriate quadrivalent or trivalent influenza vaccine should be used for individuals six months of age and older who do not have contraindications or precautions; 2) continues to strongly recommend that inactivated or recombinant influenza vaccines be offered during pregnancy, at any gestational age; and 3) strongly recommends that IIV-HD, IIV-Adj or RIV should be offered, when available, over other influenza vaccines for adults 65 years of age and older.

Authors' statement

• AG — Writing–original draft, writing–review & editing
• WS — Writing–review & editing
• JP — Writing–review & editing

The NACI Seasonal Influenza Vaccine Statement for 2024–2025 was prepared by N Sicard, A Sinilaite, W Siu, P Doyon-Plourde and J Papenburg, on behalf of the NACI Influenza Working Group, and was approved by NACI.

Competing interests

J Papenburg reports grants to his institution from MedImmune and Merck and personal fees from AstraZeneca, Enanta and Merck, all of which were outside of the submitted work.

Acknowledgements

• NACI Influenza Working Group members: J Papenburg (Chair), P De Wals, I Gemmill, J Langley, A McGeer and D Moore.

• Former members: R Harrison.

• NACI members: R Harrison (Chair), V Dubey (Vice-Chair), M Andrew, J Bettinger, N Brousseau, H Decaluwe, P De Wals, E Dubé, 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], Public Health Agency of Canada [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).

The NACI acknowledges and appreciates the contribution of F Crane, R Garno, A Gil, K Gusic, SH Lim, B Pe Benito, S Pierre, C Tremblay, R Yorke, M Tunis, C Williams and M Xi.

Funding

The work of the National Advisory Committee on Immunization is supported by the Public Health Agency of Canada.

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