Prevention of Influenza Hospitalization Among Adults in the United States, 2015-2016: Results From the US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN)

J Infect Dis. 2019 Sep 13;220(8):1265-1275. doi: 10.1093/infdis/jiy723.


Background: Evidence establishing effectiveness of influenza vaccination for prevention of severe illness is limited. The US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) is a multiyear test-negative case-control study initiated in 2015-2016 to estimate effectiveness of vaccine in preventing influenza hospitalization among adults.

Methods: Adults aged ≥18 years admitted to 8 US hospitals with acute respiratory illness and testing positive for influenza by polymerase chain reaction were cases; those testing negative were controls. Vaccine effectiveness was estimated with logistic regression adjusting for age, comorbidities, and other confounding factors and stratified by frailty, 2-year vaccination history, and clinical presentation.

Results: We analyzed data from 236 cases and 1231 controls; mean age was 58 years. More than 90% of patients had ≥1 comorbidity elevating risk of influenza complications. Fifty percent of cases and 70% of controls were vaccinated. Vaccination was 51% (95% confidence interval [CI], 29%-65%) and 53% (95% CI, 11%-76%) effective in preventing hospitalization due to influenza A(H1N1)pdm09 and influenza B virus infection, respectively. Vaccine was protective for all age groups.

Conclusions: During the 2015-2016 US influenza A(H1N1)pdm09-predominant season, we found that vaccination halved the risk of influenza-association hospitalization among adults, most of whom were at increased risk of serious influenza complications due to comorbidity or age.

Keywords: adults; case-control study; hospitalization; influenza; vaccine; vaccine effectiveness.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Adult
  • Age Factors
  • Aged
  • Case-Control Studies
  • Comorbidity
  • Female
  • Frailty / diagnosis
  • Frailty / epidemiology
  • Hospitalization / statistics & numerical data*
  • Humans
  • Influenza A virus / isolation & purification
  • Influenza B virus / isolation & purification
  • Influenza Vaccines / administration & dosage*
  • Influenza, Human / diagnosis
  • Influenza, Human / epidemiology
  • Influenza, Human / therapy*
  • Influenza, Human / virology
  • Male
  • Middle Aged
  • Sentinel Surveillance*
  • Treatment Outcome
  • United States / epidemiology
  • Vaccination / statistics & numerical data
  • Young Adult


  • Influenza Vaccines