High-Dose Influenza Vaccine to Reduce Hospitalizations

Superior protection against laboratory-confirmed influenza has been proved for high-dose inactivated influenza vaccine, as compared with the standard dose, among adults 65 years of age or older. However, data on the relative effectiveness of the high-dose vaccine against severe clinical outcomes, including hospitalizations, are limited.

We conducted a pragmatic, registry-based, open-label, randomized, active-controlled trial to evaluate the relative effectiveness of high-dose inactivated influenza vaccine, as compared with the standard dose, against severe clinical outcomes among community-dwelling adults 65 to 79 years of age. The trial was performed during two influenza seasons (2023-2024 and 2024-2025) with regional health registry data in Galicia, Spain. In each influenza season, the participants were randomly assigned in a 1:1 ratio to receive high-dose inactivated influenza vaccine or the standard dose. The primary end point was a composite of hospitalization for influenza or pneumonia from 14 days after vaccination to May 31 of the following year.

A total of 103,169 unique participants underwent randomization; 31,307 participants were enrolled in both seasons and were counted for each. During the 2023-2024 and 2024-2025 seasons, 59,490 and 74,986 participants, respectively, underwent randomization. Among the participants, the mean (±SD) age was 72.3±4.3 years, and 53.6% were men. A primary end-point event occurred in 174 of 67,093 participants (absolute risk, 0.26%) in the high-dose group and in 227 of 66,789 (absolute risk, 0.34%) in the standard-dose group (relative vaccine effectiveness, 23.7%; 95% confidence interval [CI], 6.6 to 37.7). Hospitalization for influenza occurred in 63 of 67,093 participants (absolute risk, 0.09%) in the high-dose group and in 92 of 66,789 (absolute risk, 0.14%) in the standard-dose group (relative vaccine effectiveness, 31.8%; 95% CI, 5.0 to 51.3). The incidence of serious adverse events appeared to be similar in the two trial groups.

Among community-dwelling adults 65 to 79 years of age, there appeared to be fewer hospitalizations for influenza or pneumonia with high-dose inactivated influenza vaccine than with the standard dose. (Funded by Sanofi; GALFLU ClinicalTrials.gov number NCT06141655; EudraCT number, 2023-506977-36-00.).