Introduction
Older adults face an increased risk of influenza-related intensive care unit (ICU) admission and in-hospital death (IHD). Although vaccination reduces hospitalization, its effect on these outcomes remains uncertain. We estimated the association between influenza vaccination and both outcomes among adults aged?≥65?years hospitalized with laboratory-confirmed influenza.

Research design and methods
We conducted a retrospective cohort study using European I-MOVE hospital network data (2015/16–2024/25); vaccination was defined as vaccine receipt?≥14?days before symptom onset. We estimated pooled-season adjusted risk ratios (aRR) using Poisson regression adjusting for potential confounders. We calculated relative risk reduction (RRR) as (1?aRR)×100, overall and by age group (65–79, ≥80?years).

Results
After exclusions, 4,257 patients (five study sites, six seasons) were included. ICU admission occurred in 3% of vaccinated and 5% of unvaccinated patients; IHD occurred in 5% of both groups. RRR was 11% (95% CI: ?21–34) against ICU admission (65–79?years: ?4%; ≥80?years: 44%). RRR against IHD was 26% (95% CI: 3–43); 17% and 29% in each respective age group.

Conclusions
Vaccination showed little or no association with ICU admission, but was associated with a one-quarter reduction in IHD among hospitalized older adults, reinforcing its benefits against fatal in-hospital outcomes.