Effectiveness of influenza vaccines in preventing severe influenza illness among adults: A systematic review and meta-analysis of test-negative design case-control studies

J Infect. 2017 Nov;75(5):381-394. doi: 10.1016/j.jinf.2017.09.010. Epub 2017 Sep 18.


Objectives: Summary evidence of influenza vaccine effectiveness (IVE) against hospitalized influenza is lacking. We conducted a meta-analysis of studies reporting IVE against laboratory-confirmed hospitalized influenza among adults.

Methods: We searched Pubmed (January 2009 to November 2016) for studies that used test-negative design (TND) to enrol patients hospitalized with influenza-associated conditions. Two independent authors selected relevant articles. We calculated pooled IVE against any and (sub)type specific influenza among all adults, and stratified by age group (18-64 and 65 years and above) using random-effects models.

Results: We identified 3411 publications and 30 met our inclusion criteria. Between 2010-11 and 2014-15, the pooled seasonal IVE was 41% (95%CI:34;48) for any influenza (51% (95%CI:44;58) among people aged 18-64y and 37% (95%CI:30;44) among ≥65 years). IVE was 48% (95%CI:37;59),37% (95%CI:24;50) and 38% (95%CI:23;53) against influenza A(H1N1)pdm09, A(H3N2) and B, respectively. Among persons aged ≥65 year, IVE against A(H3N2) was 43% (95%CI:33;53) in seasons when circulating and vaccine strains were antigenically similar and 14% (95%CI:-3;30) when A(H3N2) variant viruses predominated.

Conclusions: Influenza vaccines provided moderate protection against influenza-associated hospitalizations among adults. They seemed to provide low protection among elderly in seasons where vaccine and circulating A(H3N2) strains were antigenically variant.

Keywords: Adults; Hospitalization; Influenza; Meta-analysis; Systematic review; Vaccine effectiveness.

Publication types

  • Meta-Analysis
  • Review
  • Systematic Review

MeSH terms

  • Adult
  • Case-Control Studies
  • Hospitalization
  • Humans
  • Immunogenicity, Vaccine
  • Influenza Vaccines*
  • Influenza, Human / prevention & control*
  • Treatment Outcome


  • Influenza Vaccines