Relative and absolute effectiveness of high-dose and standard-dose influenza vaccine against influenza-related hospitalization among older adults - United States, 2015-2017

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Clin Infect Dis. 2020 Feb 18. pii: ciaa160. doi: 10.1093/cid/ciaa160. [Epub ahead of print] Relative and absolute effectiveness of high-dose and standard-dose influenza vaccine against influenza-related hospitalization among older adults - United States, 2015-2017.

Doyle JD¹, Beacham L^1,2, Martin ET³, Talbot HK⁴, Monto A³, Gaglani M⁵, Middleton DB⁶, Silveira FP⁶, Zimmerman RK⁶, Alyanak E^1,2, Smith ER^1,7, Flannery BL¹, Rolfes M¹, Ferdinands JM¹.
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Abstract

BACKGROUND:

Seasonal 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.
METHODS:

Hospitalized patients with acute respiratory illness were enrolled in an observational vaccine effectiveness study at eight 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.
RESULTS:

Among 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%).
CONCLUSIONS:

During two U.S. 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. This work is written by (a) US Government employee(s) and is in the public domain in the US.


PMID: 32067049 DOI: 10.1093/cid/ciaa160