Cochrane: flu vaccine offers modest protection in healthy adults

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Takeaway

  • Updated Cochrane review demonstrates that inactivated influenza vaccine confers modest reduction in the proportion of illness and influenza-like illness (ILI) in healthy adults (including pregnant women).

Why this matters

  • Adults receiving inactivated parenteral influenza vaccination have a small but nevertheless important influenza and ILI risk reduction during a specific season.
  • Clinicians should continue to recommend/offer vaccination during routine office visits.

Key results

  • 52 trials in >80,000 adults (mostly focused on 25 inactivated vaccine studies).
  • Inactivated parenteral vaccine was shown to reduce influenza risk from 2.3% to 1%, with a 59% efficacy and numbers needed to vaccinate (NNV) of 71 (risk ratio [RR], 0.41; 95% CI, 0.36-0.47; moderate-certainty evidence).
  • Inactivated vaccine effectiveness for ILI prevention was 16% (RR, 0.84; 95% CI, 0.75-0.95; moderate-certainty evidence; NNV, 29).
  • Trivalent inactivated vaccine (with pH1N1) was weakly protective in mothers within 24 weeks after delivery (vaccine effectiveness, 50%; 95% CI, 14%-71%); ILI protection was not statistically significant.
  • Evidence for reduction in lost working days or hospitalization was of "low certainty."

Study design

  • Cochrane update evaluating effects of live, attenuated, or killed influenza vaccines (or fractions thereof) in healthy adults.
  • Funding: NIH.

Limitations

  • Inactivated vaccine safety data are sparse.
  • Publication bias.
  • Observational immortal time bias (pregnancy data).