tetano
Editor, Senior Moderator
Can Commun Dis Rep
. 2026 Jun 30;52(6):231-245.
doi: 10.14745/ccdr.v52i06a03. eCollection 2026 Jun.
Intraseasonal waning of influenza vaccine effectiveness and implications for the optimal timing of seasonal vaccination programs: A scoping review
Pamela Doyon-Plourde[SUP] 1 [/SUP], Fazia Tadount[SUP] 1 2 [/SUP], Anabel Gil[SUP] 1 [/SUP], Calin Lazarescu[SUP] 1 [/SUP], Marie-Michelle Ursu[SUP] 1 2 [/SUP], Nadine Sicard[SUP] 1 [/SUP], Winnie Siu[SUP] 1 3 [/SUP], Angela Sinilaité[SUP] 1 [/SUP]
Affiliations
Background: Seasonal influenza vaccination programs aim to provide protection before the virus circulation begins. However, vaccine effectiveness (VE) may decline within a single influenza season due to waning immunity, antigenic drift, and season-specific factors, raising questions about optimal vaccination timing. The purpose of this review was to synthesize evidence on intraseasonal waning of seasonal influenza VE and examine the implications and key considerations for optimizing the timing of seasonal vaccination in Canada.
Methods: A scoping review was conducted, with searches of MEDLINE, Embase, Scopus, Cochrane Library, and ProQuest Public Health Database that identified studies published from 2010 to June 2024, with an update in July 2025. Eligible studies included clinical trials, observational studies, systematic reviews, and modelling studies reporting at least two VE estimates by time since vaccination within a season or assessing vaccination timing and its impact on influenza outcomes.
Results: Forty-nine studies met inclusion criteria, including 37 assessing intraseasonal waning and 12 examining vaccination timing. Overall, VE was generally highest within one to three months post-vaccination and declined over the season (e.g., three to six months post-vaccination). Waning was more consistently observed for influenza A, particularly A(H3N2), and among adults aged 60 years and older. Modelling studies suggested that delaying vaccination could reduce influenza burden under select late-peaking or fast-waning scenarios; however, estimated benefits were generally small and highly sensitive to assumptions.
Conclusion: Intraseasonal waning of influenza VE is consistently observed, particularly for influenza A and in older adults, but represents a gradual decline that does not typically undermine season-long effectiveness. Evidence does not support substantial or consistent population-level benefits from delaying vaccination.
Keywords: duration of protection; influenza vaccine; optimal timing; vaccine effectiveness; waning.
. 2026 Jun 30;52(6):231-245.
doi: 10.14745/ccdr.v52i06a03. eCollection 2026 Jun.
Intraseasonal waning of influenza vaccine effectiveness and implications for the optimal timing of seasonal vaccination programs: A scoping review
Pamela Doyon-Plourde[SUP] 1 [/SUP], Fazia Tadount[SUP] 1 2 [/SUP], Anabel Gil[SUP] 1 [/SUP], Calin Lazarescu[SUP] 1 [/SUP], Marie-Michelle Ursu[SUP] 1 2 [/SUP], Nadine Sicard[SUP] 1 [/SUP], Winnie Siu[SUP] 1 3 [/SUP], Angela Sinilaité[SUP] 1 [/SUP]
Affiliations
- PMID: 42592326
- PMCID: PMC13465922
- DOI: 10.14745/ccdr.v52i06a03
Background: Seasonal influenza vaccination programs aim to provide protection before the virus circulation begins. However, vaccine effectiveness (VE) may decline within a single influenza season due to waning immunity, antigenic drift, and season-specific factors, raising questions about optimal vaccination timing. The purpose of this review was to synthesize evidence on intraseasonal waning of seasonal influenza VE and examine the implications and key considerations for optimizing the timing of seasonal vaccination in Canada.
Methods: A scoping review was conducted, with searches of MEDLINE, Embase, Scopus, Cochrane Library, and ProQuest Public Health Database that identified studies published from 2010 to June 2024, with an update in July 2025. Eligible studies included clinical trials, observational studies, systematic reviews, and modelling studies reporting at least two VE estimates by time since vaccination within a season or assessing vaccination timing and its impact on influenza outcomes.
Results: Forty-nine studies met inclusion criteria, including 37 assessing intraseasonal waning and 12 examining vaccination timing. Overall, VE was generally highest within one to three months post-vaccination and declined over the season (e.g., three to six months post-vaccination). Waning was more consistently observed for influenza A, particularly A(H3N2), and among adults aged 60 years and older. Modelling studies suggested that delaying vaccination could reduce influenza burden under select late-peaking or fast-waning scenarios; however, estimated benefits were generally small and highly sensitive to assumptions.
Conclusion: Intraseasonal waning of influenza VE is consistently observed, particularly for influenza A and in older adults, but represents a gradual decline that does not typically undermine season-long effectiveness. Evidence does not support substantial or consistent population-level benefits from delaying vaccination.
Keywords: duration of protection; influenza vaccine; optimal timing; vaccine effectiveness; waning.