Influenza: how do previous vaccination and infection moderate risk?

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  • 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.

Study design

  • 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.

Key results

  • 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.