• Joshua D Doyle, Lauren Beacham, Emily T Martin, H Keipp Talbot, Arnold Monto, Manjusha Gaglani, Donald B Middleton, Fernanda P Silveira, Richard K Zimmerman, Elif Alyanak, Emily R Smith, Brendan L Flannery, Melissa Rolfes, and Jill M Ferdinands.
• Influenza Division, US Centers for Disease Control and Prevention, Atlanta, Georgia, USA.
• Clin. Infect. Dis. 2021 Mar 15; 72 (6): 995-1003.

BackgroundSeasonal influenza causes substantial morbidity and mortality in older adults. High-dose inactivated influenza vaccine (HD-IIV), with increased antigen content compared to standard-dose influenza vaccines (SD-IIV), is licensed for use in people aged ≥65 years. We sought to evaluate the effectiveness of HD-IIV and SD-IIV for prevention of influenza-associated hospitalizations.MethodsHospitalized patients with acute respiratory illness were enrolled in an observational vaccine effectiveness study at 8 hospitals in the United States Hospitalized Adult Influenza Vaccine Effectiveness Network during the 2015-2016 and 2016-2017 influenza seasons. Enrolled patients were tested for influenza, and receipt of influenza vaccine by type was recorded. Effectiveness of SD-IIV and HD-IIV was estimated using a test-negative design (comparing odds of influenza among vaccinated and unvaccinated patients). Relative effectiveness of SD-IIV and HD-IIV was estimated using logistic regression.ResultsAmong 1487 enrolled patients aged ≥65 years, 1107 (74%) were vaccinated; 622 (56%) received HD-IIV, and 485 (44%) received SD-IIV. Overall, 277 (19%) tested positive for influenza, including 98 (16%) who received HD-IIV, 87 (18%) who received SD-IIV, and 92 (24%) who were unvaccinated. After adjusting for confounding variables, effectiveness of SD-IIV was 6% (95% confidence interval [CI] -42%, 38%) and that of HD-IIV was 32% (95% CI -3%, 54%), for a relative effectiveness of HD-IIV versus SD-IIV of 27% (95% CI -1%, 48%).ConclusionsDuring 2 US influenza seasons, vaccine effectiveness was low to moderate for prevention of influenza hospitalization among adults aged ≥65 years. High-dose vaccine offered greater effectiveness. None of these findings were statistically significant.Published by Oxford University Press for the Infectious Diseases Society of America 2020.

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