Summary of National Advisory Committee on Immunization (NACI) statement: Recommendation on repeated seasonal influenza vaccination

An Advisory Committee Statement (ACS)
National Advisory Committee on Immunization (NACI)

On this page

• Overview
• What you need to know

Overview

• On February 21, 2023, the Public Health Agency of Canada (PHAC) released recommendations from the National Advisory Committee on Immunization (NACI) on repeated seasonal influenza vaccination. This guidance is based on current evidence and NACI expert opinion.
• Some studies published since the 1970s have raised questions about whether repeated seasonal influenza vaccination (e.g., receiving the seasonal influenza vaccine more than one year in a row) may reduce the protection provided by the vaccine in the most recent season that was studied.
• After reviewing the available evidence on repeated seasonal influenza vaccination, NACI determined that in general, there was no significant difference in vaccine efficacy or effectiveness between vaccination in two consecutive seasons compared to vaccination only in the most recent season at the time of the study.
• Multiple sources of evidence show that repeated influenza vaccination, including in the most recent seasons, is more effective than no vaccination in the most recent season.
• NACI continues to strongly recommend that the seasonal influenza vaccine should be offered annually to everyone 6 months of age and older who does not have contraindications to the vaccine, regardless of whether they received the seasonal influenza vaccine in previous seasons.
• As risks are higher in some settings and for some individuals, influenza immunization is particularly important for the following groups:
  • People at higher risk of severe disease, hospitalization and influenza-related complications, including
    • Children 6 to 59 months of age
    • Adults 65 years of age and older
    • Adults and children with certain chronic health conditions
    • Individuals who are pregnant
    • People of any age who are residents of nursing homes and other chronic care facilities
    • Indigenous peoples
  • People who can pass influenza to those at higher risk, including
    • Healthcare and other care providers
    • Household contacts of people at highest risk
    • Child care workers for children less than 5 years of age
  • People who provide essential community services; and
  • People in direct contact with poultry who could become infected with avian influenza during culling operations.
• NACI will continue to monitor the evolving evidence and will update guidance as needed.

For the full statement, including supporting evidence and rationale, please see NACI Statement: Recommendation on repeated seasonal influenza vaccination.

For a full list of people who are particularly recommended to receive the influenza vaccine, please see Priority Groups for Influenza Vaccination in the Canadian Immunization Guide Chapter on Influenza and Statement on Seasonal Influenza Vaccine for 2022-2023.

For more information on NACI recommendations related to seasonal influenza vaccination, please see the Canadian Immunization Guide Chapter on Influenza and Statement on Seasonal Influenza Vaccine for 2022-2023.

What you need to know

• Influenza is a contagious respiratory illness caused by influenza viruses. Consistent with many other respiratory viruses, the circulation of seasonal influenza viruses increases in the fall and winter months as people spend more time together indoors.
• Influenza can cause illness ranging from mild to severe and can result in hospitalization and sometimes death. Prior to the COVID-19 pandemic, seasonal influenza led to an estimated average of 12,200 hospitalizations and 3,500 deaths in Canada every year. As of November 2022, Canada was experiencing a 2022-2023 seasonal influenza epidemic with activity above expected levels typical of that time of year.
• Some populations, including young children, older adults, people with chronic health conditions and people who are pregnant, may be at higher risk for serious influenza complications, like pneumonia and worsening of underlying medical conditions, such as heart disease.
• The seasonal influenza vaccine is the most effective way to help prevent influenza and influenza-related complications. The influenza vaccine can also help prevent the spread of influenza to others.
• The seasonal influenza vaccine is recommended every year because protection from the vaccine decreases over time and the strains of the influenza viruses that circulate change from year to year. Before every influenza season, international experts provide advice on the strains of influenza viruses that should be included in the vaccine for the upcoming season.
• Influenza vaccine protection each year is influenced by a number of factors that may include the match between the vaccine strains and the circulating strains, the age and underlying health status of the vaccine recipient and the type of influenza vaccine received. As well, the influenza strain of a person's first exposure to the influenza virus may influence how they respond to influenza vaccination and infection over the course of their lifetime. The importance of repeated vaccination on vaccine effectiveness is an important topic, and some studies since the 1970s have suggested a possible negative impact of prior influenza vaccination on vaccine effectiveness in some seasons. Additional study on this topic would be helpful. NACI will continue to monitor the evidence and will update guidance as needed.
• Overall, NACI's evidence review showed no significant difference in the effectiveness of repeated influenza vaccination across two consecutive seasons compared to vaccination in the current season only. Of all the seasons investigated across many studies, only during two influenza seasons (2010-2011 and 2014-2015) was repeated vaccination across two consecutive seasons associated with a reduced effectiveness in the most recent season compared to vaccination in that season only. Reduced effectiveness in the 2010-2011 and 2014-2015 influenza seasons with consecutive season vaccination were both against the influenza A (H3N2) virus.
• Multiple sources of evidence consistently show that repeated seasonal influenza vaccination, including in the current season, is more effective than no vaccination in the current season.
• Receiving the influenza vaccine can reduce the chances of being co-infected with influenza and other serious respiratory virus infections at the same time. Preventing influenza by receiving the seasonal influenza vaccine will also help to reduce stress on the health system during the respiratory virus season and while COVID-19 continues to circulate.
• For individuals 6 months of age or older, NACI recommends that seasonal influenza vaccines (including live and non-live vaccines) may be given at the same time as, or at any time before or after, COVID-19 vaccines. This will help to facilitate influenza and COVID-19 vaccine programs in the fall and winter months.
• PHAC has published additional guidance on the administration of the seasonal influenza vaccine in the context of the COVID-19 pandemic to support provincial and territorial vaccine programs and primary care providers. For more information, please see Guidance on the use of influenza vaccine in the presence of COVID-19.

For the full statement, including supporting evidence and rationale, please see NACI Statement: Recommendation on repeated seasonal influenza vaccination.