Helene Bricout, Marie-Cecile Levant, Pascal Crépey, Gaëtan Gavazzi, Jacques Gaillat, Marine Dufournet, Nada Assi, Benjamin Grenier, Fanny Raguideau, Camille Salamand, Anne Mosnier, Laurence Watier, Odile Launay, Matthew Loiacono
HD vaccine was associated with a significant reduction in influenza-related hospitalisations in French nursing home residents, supporting preferential HD use in this high-risk population. Residual confounding cannot be excluded, and vaccine safety was not assessed in the present analysis.
BACKGROUND: Older adults in nursing homes face high influenza-related morbidity and mortality due to immunosenescence and comorbidities, which may reduce vaccine effectiveness. High-dose (HD) influenza vaccine, containing four times more antigen than standard-dose (SD) formulations, aim to compensate for this impaired immune response.
OBJECTIVES: To compare the Relative Vaccine Effectiveness (rVE) of HD versus SD influenza vaccines against influenza-related hospitalisations (primary), and hospitalisations due to pneumonia or combined influenza/pneumonia (secondary) in nursing home residents aged ≥65 years.
STUDY DESIGN: Nationwide retrospective cohort (French SNDS). Residents vaccinated between 1 September 2022, and 31 March 2023, were followed until 30 June 2023, discharge or death. Facilities with in-house pharmacies were excluded.
EXPOSURES/OUTCOMES: HD vs. SD influenza vaccine (pharmacy dispensing codes). Hospitalisations identified by ICD-10 discharge codes.
METHODS: HD and SD recipients were matched 1:1 using propensity scores with exact matching on sex, age group, region and vaccination week. Incidence rate ratios (IRR) were estimated using Poisson/negative binomial models. rVE = (1-IRR) × 100.
RESULTS: Among 315 239 residents (123 720 HD; 191 519 SD), 76 858 pairs were matched (mean age 88 years; 75% women). Influenza hospitalisation rates were 302 vs. 438 per 100 000 person-years, corresponding to an rVE of 30.8% (95% CI: 11.8-45.7; P = .0029). No significant rVE was observed for pneumonia or combined outcomes.
CONCLUSIONS AND RELEVANCE: HD vaccine was associated with a significant reduction in influenza-related hospitalisations in French nursing home residents, supporting preferential HD use in this high-risk population. Residual confounding cannot be excluded, and vaccine safety was not assessed in the present analysis.