Relative Effectiveness of High-Dose vs. Standard-Dose Influenza Vaccines in Preventing Hospitalizations: A National Retrospective Cohort Study in France, 2022/2023 Season.

BACKGROUND: A French cohort study (2021/2022 influenza season) found the high-dose influenza vaccine (HD) more effective than standard-dose vaccines (SDs) in preventing influenza-related hospitalizations in the elderly. The study continued to refine results and validate these findings. METHODS: Data from community-dwelling 65+ adults who received HD or SD during the 2022/2023 vaccination campaign were extracted from the National Health database. Hospitalizations were recorded from 14 days postvaccination until June 30, 2023. HD and SD recipients were matched using a propensity score. Associations between vaccines and hospitalizations were assessed by estimating incidence rate ratios and converting them to HD vs. SD vaccine relative effectiveness (rVE). RESULTS: A total of 675,412 HD recipients were matched to 2,701,648 SD recipients. The rVE for influenza-related hospitalizations was 27.4% [95% CI: 19.8; 34.3]. It ranged from 22.7% [9.8; 33.6] to 33.6% [21.2; 44.0] across age groups, indicating that HD consistently outperformed SDs in preventing influenza-related hospitalizations, with the highest effect observed in 85+. CONCLUSIONS: Our study is the first to publish rVE data comparing HD and SDs in a real-world setting in France for the 2022/2023 influenza season. Its findings reaffirm the benefit of HD vs. SDs. HD could help reduce the burden of severe respiratory infections in the elderly.