CDC: influenza vaccine efficacy at 47% in adults, 61% in kids

  • Doyle JD & al.
  • MMWR Morb Mortal Wkly Rep
  • 15 Feb 2019

  • curated by Liz Scherer
  • Clinical Essentials
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  • Interim reports from CDC estimate that overall influenza vaccine effectiveness (VE) is 47% against laboratory-confirmed, medically attended influenza; higher VE seen in children.
  • Companion report shows influenza activity remains elevated, with A(H1N1) strain predominating nationwide; A(H3N2) predominates in Southeastern states.

Why this matters

  • Vaccination remains the most effective preventive tool against influenza-related illness, complications, and deaths, but improved coverage is needed to realize full potential.
  • Continue to offer/encourage vaccination to all unvaccinated patients ages >6 months as long as influenza viruses are circulating.

Key results

  • 14% (465/3245) of children/adults with acute respiratory infections (ARI) tested positive for influenza (98% influenza A, 2% influenza B).
  • 74% (293), 26% (101) of 394 subtyped influenza A viruses were A(H1N1)pdm09, A(H3N2), respectively.
  • Overall, 43% (198), 57% (1591) vaccinated persons were influenza-positive, -negative, respectively.
  • Adjusted VE against all medically attended influenza virus-associated ARI: 47% (95% CI, 34%-57%).
  • Adjusted VE for children, ages 6 months to 17 years: 61% (95% CI, 44%-73%).

Study design

  • Interim US Flu VE Network surveillance report evaluating VE against laboratory-confirmed influenza associated with medically attended ARI, November 23, 2018-February 2, 2019.
  • Funding: CDC.


  • Small sample size.
  • Self-report bias; end-of-season VE may differ.
  • Observational.
  • Data limited to outpatient medical visits vs severe complications/hospitalizations.

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