Association between influenza vaccination and severe outcomes in adults aged ≥ 65 years hospitalized with laboratory-confirmed influenza: a retrospective cohort study, I-MOVE hospital network, Europe, 2015/16–2024/25

Résumé fourni par la source

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. 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). 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. 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. Older adults hospitalized with influenza may experience severe outcomes, such as admission to an intensive care unit (ICU) or death during their hospital stay. While influenza vaccines are known to reduce the risk of hospitalization, it is less clear whether they also reduce the risk of these severe outcomes once someone is already hospitalized. We analyzed data from a large European hospital network that collected information over several influenza seasons between 2015 and 2025. The study included 4,257 adults aged 65 years and older who were admitted to hospital and tested positive for influenza virus. We compared the risk of severe outcomes between vaccinated and unvaccinated people. Among vaccinated people positive for influenza virus, about 3 in 100 were admitted to an ICU, compared with about 5 in 100 unvaccinated people. Death in hospital occurred in about 5 in 100 people in both groups. After taking age, sex, long-term health conditions, timing of admission, season and study site into account, vaccination showed little or no clear association with ICU admission. In contrast, vaccinated individuals had a lower risk of dying in hospital than unvaccinated individuals. This corresponded to about a one-quarter reduction in the risk of death. This finding suggests that influenza vaccination may provide additional benefits in reducing the risk of death among older adults who are hospitalized with influenza, even when hospital admission is not prevented, supporting continued efforts to improve vaccine uptake in this high-risk population.

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