Relative effectiveness of high-dose vs standard-dose influenza vaccines in preventing hospitalizations: a national retrospective cohort study in France, 2022/23 season

BackgroundA French retrospective observational cohort study conducted during the 2021/22 influenza season found that the high-dose influenza vaccine (HD) was more effective than standard-dose vaccines (SDs) in preventing influenza-related hospitalizations in the elderly. The study continued during the 2022/23 season to obtain more accurate results and validate the findings during a different influenza season. Material and methodsData from community-dwelling 65+ adults vaccinated with HD or SD during the 2022/23 vaccination campaign were extracted from the National Health database. Hospitalizations were recorded from 14 days after vaccination until 30 June 2023. HD and SD recipients were matched using a propensity score with an exact constraint on age, sex, vaccination week, and geographical region. Associations between vaccines and hospitalizations (influenza or non-influenza related) were assessed by estimating incidence rate ratios and converting them to HD vs SD vaccine relative effectiveness (rVE). Results675,412 HD recipients were matched to 2,701,648 SD recipients. The HD vs SD rVE for influenza-related hospitalizations was 27.39% [95%CI: 19.79;34.27]. It ranged from 22.65% [9.84;33.64] to 33.55% [21.19;43.98] across age groups, indicating that HD resulted in consistently better protection than SDs against influenza-related hospitalizations in all age groups, with the highest effect observed in 85+. ConclusionOur study is the first to publish rVE data comparing HD and SD in France, for the 2022/23 influenza season. Its findings reaffirm the benefit of HD vs SD in reducing influenza-related hospitalizations in a real-world setting. HD could help reduce the burden of severe respiratory infections in the elderly. Registration number: Not applicable. HighlightsO_ST_ABSTake-home messageC_ST_ABSIn France, during the 2022/23 influenza season, the high-dose vaccine has reduced influenza-related hospitalizations by 27.4% compared to standard-dose vaccines among community-dwelling 65+ adults, with a clinical benefit observed across all age groups.