- Prior season influenza vaccination reduced vaccine effectiveness (VE), but not in patients with previous season infection.
Why this matters
- Accumulating evidence indicates repeated influenza vaccination negatively affects VE; however, this has not been examined in the context of previous influenza infection.
- Prospective, population-based, single-center.
- Outpatients with influenza-like illness (ILI) over 3 consecutive seasons (2009-2012).
- Prior trivalent inactivated influenza vaccination (TIV) and medically attended influenza A (MA-fluA) status collected.
- Test-negative case-control design to estimate VE of current-season TIV against MA-fluA in the context of prior season infection.
- Funding: JSPS KAKENHI Grant-in-Aid for Young Scientists.
- 5838 ILI episodes (4127 participants), including 1896 rapid diagnostic test (RDT) positive and 3942 negative.
- Profound protective effect of prior season MA-fluA against current season MA-fluA (adjusted OR, 0.38).
- Significantly lower VE in prior season vaccinated vs unvaccinated participants, but only in those without prior season MA-fluA (13% vs 44%; P<.05).
- Relied on RDTs which are not as sensitive and specific as reverse transcription polymerase chain reaction.
- No influenza A subtyping.
- Did not collect vaccination history for influenza A (H1N1) 2009pdm.