Efficacy of High-Dose Versus Standard-Dose Influenza Vaccine in Older Adults

Study Questions:

In adults 65 years of age or older, what is the efficacy of the high-dose, trivalent, inactivated influenza vaccine (IIV3-HD), compared with standard-dose vaccine (IIV3-HD), for the prevention of laboratory-confirmed influenza illness?


This was a phase IIIb-IV, multicenter, randomized, double-blind, active-controlled trial in which IIV3-HD was compared with IIV3-SD. Persons 65 years of age or older were recruited from 126 centers in the United States and Canada. The primary endpoint of the study was the occurrence, at least 14 days after vaccination, of laboratory-confirmed influenza; assessments of safety and immunogenicity were also performed. Endpoints were evaluated during 2011-2012 (year 1) and the 2012-2013 (year 2) northern-hemisphere influenza seasons.


A total of 31,989 participants were enrolled. Five hundred and twenty-nine participants met the primary endpoint with 228 (1.4%) in the IIV3-HD group and 301 (1.9%) in the IIV3-SD group. The relative efficacy of IIV3-HD, compared to IIV3-SD, was 24.2%. During monitoring for safety (approximately 6-8 months after vaccination), 1,323 participants (8.3%) in the IIV3-HD and 1,442 participants (9.0%) in the IIV3-SD group had at least one serious adverse event (relative risk, 0.92; 95% confidence interval, 0.85-0.99).


The authors concluded that in older adults, IIV3-HD provided significantly improved protection against laboratory-confirmed influenza illness, compared to IIV3-SD.


This is an important study that demonstrates a clinical benefit, in terms of relative efficacy, of IIV3-HD, compared to IIV3-SD, in older adults. Given the burden of influenza in this population and the need for improved vaccination in older adults, these findings are important and relevant, and may translate into larger public health benefits.

Clinical Topics: Prevention

Keywords: Risk, Influenza, Human, Safety, Canada, Vaccines, Inactivated, Confidence Intervals, Vaccination, United States

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