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. 2021 Jul 2;224(1):151-163.
doi: 10.1093/infdis/jiaa772.

Vaccine Effectiveness Against Influenza-Associated Hospitalizations Among Adults, 2018-2019, US Hospitalized Adult Influenza Vaccine Effectiveness Network

Jill M Ferdinands  1 , Manjusha Gaglani  2 , Shekhar Ghamande  2 , Emily T Martin  3 , Donald Middleton  4 , Arnold S Monto  3 , Fernanda Silveira  4 , Helen K Talbot  5 , Richard Zimmerman  4 , Emily R Smith  1 , Manish Patel  1 ; US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) Study Investigators
Collaborators, Affiliations

Vaccine Effectiveness Against Influenza-Associated Hospitalizations Among Adults, 2018-2019, US Hospitalized Adult Influenza Vaccine Effectiveness Network

Jill M Ferdinands et al. J Infect Dis. .

Abstract

We estimated vaccine effectiveness (VE) for prevention of influenza-associated hospitalizations among adults during the 2018-2019 influenza season. Adults admitted with acute respiratory illness to 14 hospitals of the US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN) and testing positive for influenza were cases; patients testing negative were controls. VE was estimated using logistic regression and inverse probability of treatment weighting. We analyzed data from 2863 patients with a mean age of 63 years. Adjusted VE against influenza A(H1N1)pdm09-associated hospitalization was 51% (95% confidence interval [CI], 25%-68%). Adjusted VE against influenza A(H3N2) virus-associated hospitalization was -2% (95% CI, -65% to 37%) and differed significantly by age, with VE of -130% (95% CI, -374% to -27%) among adults 18 to ≤56 years of age. Although vaccination halved the risk of influenza A(H1N1)pdm09-associated hospitalizations, it conferred no protection against influenza A(H3N2)-associated hospitalizations. We observed negative VE for young and middle-aged adults but cannot exclude residual confounding as a potential explanation.

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

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Figures

Figure 1.
Figure 1.
Adjusted vaccine effectiveness against influenza A(H3N2)–associated hospitalizations among adults by participant age (years), US Hospitalized Adult Influenza Vaccine Effectiveness Network (HAIVEN), 2018–2019 (n = 2304). Abbreviations: CI, confidence interval; VE, vaccine effectiveness.
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