Abstract
BackgroundResults of previous influenza vaccination effects on current season influenza vaccine effectiveness (VE) are inconsistent.ObjectivesTo explore previous influenza vaccination effects on current season VE among population targeted for vaccination.MethodsWe used 2011/2012 to 2016/2017 I‐MOVE primary care multicentre test‐negative data. For each season, we compared current season adjusted VE (aVE) between individuals vaccinated and unvaccinated in previous season. Using unvaccinated in both seasons as a reference, we then compared aVE between vaccinated in both seasons, current only, and previous only.ResultsWe included 941, 2645 and 959 influenza‐like illness patients positive for influenza A(H1N1)pdm09, A(H3N2) and B, respectively, and 5532 controls. In 2011/2012, 2014/2015 and 2016/2017, A(H3N2) aVE point estimates among those vaccinated in previous season were −68%, −21% and −19%, respectively; among unvaccinated in previous season, these were 33%, 48% and 46%, respectively (aVE not computable for influenza A(H1N1)pdm09 and B). Compared to current season vaccination only, VE for both seasons' vaccination was (i) similar in two of four seasons for A(H3N2) (absolute difference [ad] 6% and 8%); (ii) lower in three of four seasons for influenza A(H1N1)pdm09 (ad 18%, 26% and 29%), in two seasons for influenza A(H3N2) (ad 27% and 39%) and in two of three seasons for influenza B (ad 26% and 37%); (iii) higher in one season for influenza A(H1N1)pdm09 (ad 20%) and influenza B (ad 24%).ConclusionsWe did not identify any pattern of previous influenza vaccination effect. Prospective cohort studies documenting influenza infections, vaccinations and vaccine types are needed to understand previous influenza vaccinations' effects.
Highlights
Constant evolution of influenza viruses requires possible reformulation of the influenza vaccine every season
In 2011/12, 2014/15, 2016/17 A(H3N2) adjusted VE (aVE) point estimates among those vaccinated in previous season, were -68%, - 21% and -19% respectively; among unvaccinated in previous season 33%, 48%, 46% respectively (aVE not computable for influenza A(H1N1)pdm09 and B)
In this article, using the I-MOVE primary care multicentre case-control study (MCCS) data, we present, influenza type/subtype-specific vaccine effectiveness (VE) stratified by previous season vaccination among the target groups for vaccination for each of the 2011/12 to 2016/17 seasons
Summary
Constant evolution of influenza viruses requires possible reformulation of the influenza vaccine every season. In this article, using the I-MOVE primary care multicentre case-control study (MCCS) data, we present, influenza type/subtype-specific VE stratified by previous season vaccination among the target groups for vaccination for each of the 2011/12 to 2016/17 seasons Using those unvaccinated in both seasons as a reference group, we calculated VE for different combinations of previous/current vaccination among the target population for vaccination (indicator analysis). The indicator analysis gives information on the potential residual protection of the previous season vaccination and the combined protection of current and previous season vaccination, compared to the reference group This reference group “unvaccinated in both seasons” may consist of a population that is quite different from the other categories of individuals who have been vaccinated, making controlling for confounding challenging [11]. Results of previous influenza vaccination effects on current season influenza vaccine effectiveness (VE) are inconsistent
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