1. High-dose influenza vaccination significantly reduced the incidence of influenza illness in adults 65 years of age or older when compared with the standard-dose vaccine.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Seasonal influenza remains a major cause of morbidity and mortality, particularly amongst individuals 65 years of age or older. While vaccination remains one of the most effective interventions against influenza, individuals 65 years of age and older have poorer responses to influenza vaccines and poorer protection against the virus. Efforts have been directed towards improving protection amongst these individuals. The purpose of this trial was to assess the efficacy of a high-dose, trivalent, inactivated influenza vaccine (IIV3-HD) that contains four times the hemagglutinin (HA) compared to standard-dose vaccines in preventing influenza illness in individuals 65 years of age or older.
IIV3-HD was shown to be superior to the standard-dose vaccine in preventing influenza illness amongst adults 65 years of age or older. Additionally, the incidence of serious adverse events was significantly lower in the IIV3-HD group. Notably, the study was funded by Sanofi Pasteur.
In-Depth [randomized controlled trial]: This phase IIIb-IV randomized, controlled trial compared IIV3-HD with a standard-dose vaccine in preventing cases of influenza illness in individuals 65 years of age or older. The trial was conducted at 126 centres across Canada and the United States. Patients were eligible for the study if they were at least 65 years of age without moderate or severe acute illnesses. A total of 31,989 individuals were enrolled and randomized in a 1:1 ratio to receive either IIV3-HD (i.e., 60 μg of HA per strain) or the standard-dose vaccine (i.e., 15 μg of HA per strain). Participants were instructed to contact their study site if they developed respiratory symptoms and site staff subsequently collected a nasopharyngeal swab 5 days after the onset of illness. The primary endpoint was the occurrence of laboratory-confirmed influenza illness 14 days after vaccination.
A total of 228 participants in the IIV3-HD group (1.4%) and 301 in the standard-dose group (1.9%) had laboratory-confirmed influenza–this met the predefined criteria for superiority (relative efficacy, 24.2%; 95% CI, 9.7 to 36.5). The incidence of serious adverse events was significantly lower in the IIV3-HD group as compared with the standard-dose group (RR, 0.92; 95% CI, 0.85 to 0.99). The mortality rates in the two groups were not significantly different.
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