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

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

Jill M Ferdinands  1 , Manjusha Gaglani  2 , Emily T Martin  3 , Don Middleton  4 , Arnold S Monto  3 , Kempapura Murthy  5 , Fernanda P Silveira  4 , H Keipp Talbot  6 , Richard Zimmerman  4 , Elif Alyanak  1 , Courtney Strickland  1 , Sarah Spencer  1 , Alicia M Fry  1 ; HAIVEN Study Investigators
Collaborators, Affiliations

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

Jill M Ferdinands et al. J Infect Dis. .

Abstract

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.

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Figures

Figure 1.
Figure 1.
US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) study enrollment and influenza case status, 2015–2016.
Figure 2.
Figure 2.
Adjusted vaccine effectiveness against influenza A or B virus–associated hospitalization (A) (P = .68 for interaction between vaccination status and age) and against influenza A(H1N1)pdm09 virus–associated hospitalization (B) (P = .43 for interaction) by age, US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) study, 2015–2016 (n = 1467). Abbreviations: CI, confidence interval; VE, vaccine effectiveness.
Figure 3.
Figure 3.
Variation in estimated vaccine effectiveness (against influenza A or B virus–associated hospitalization) with alternative definitions of vaccination status, US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) study, 2015–2016. The primary analysis of vaccine effectiveness used is “E. Documented or self-report with date and location.”
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