Methods: Hospitalized patients with acute respiratory illness were enrolled in an observational vaccine effectiveness study at eight hospitals in four states participating in the United States Hospitalized Adult Influenza Vaccine Effectiveness Network during the 2015-2016 and 2016-2017 influenza seasons. Predominant influenza A virus subtypes were H1N1 and H3N2, respectively, during these seasons. All enrolled patients were tested for influenza virus with polymerase chain reaction. Receipt and type of influenza vaccine was determined from electronic records and chart review. Odds of laboratory-confirmed influenza were compared among vaccinated and unvaccinated patients. Relative odds of laboratory-confirmed influenza were determined for patients who received IIV-HD or IIV-SD, and adjusted for potential confounding variables via logistic regression.
Results: Among 1744 enrolled patients aged ≥ 65 years, 1105 (63%) were vaccinated; among those vaccinated, 621 (56%) received IIV-HD and 484 (44%) received IIV-SD. Overall, 315 (18%) tested positive for influenza, including 97 (6%) who received IIV-HD, 86 (5%) who received IIV-SD, and 132 (8%) who were unvaccinated. Controlling for age, race, sex, enrollment site, date of illness, index of comorbidity, and influenza season, the adjusted odds of influenza among patients vaccinated with IIV-HD versus IIV-SD were 0.72 (p = 0.06, 95% CI: 0.52 to 1.01).
Conclusion: Comparison of high-dose versus standard-dose vaccine effectiveness during two recent influenza seasons (one H1N1 and one H3N2-predominant) suggested relative benefit (non-significant) of high-dose influenza vaccine in protecting against influenza-associated hospitalization among persons aged 65 years and older; additional years of data are needed to confirm this finding.
E. Alyanak, None
M. Gaglani, None
E. T. Martin, None
D. Middleton, None
F. P. Silveira, None
H. K. Talbot, Sanofi Pasteur: Investigator , Research grant . Gilead: Investigator , Research grant . MedImmune: Investigator , Research grant . Vaxinnate: Safety Board , none . Seqirus: Safety Board , none .
R. Zimmerman, None
B. Flannery, None
J. M. Ferdinands, None