Influenza vaccination is associated with reduced severity of community-acquired pneumonia.

Pneumonia is an important cause of influenza-associated morbidity and mortality. Influenza vaccination has been shown to reduce morbidity and mortality during influenza seasons. Protection from severe pneumonia may contribute to the beneficial effect of influenza vaccination. Therefore, we investigated the impact of prior influenza vaccination on disease severity and mortality in patients with community-acquired pneumonia (CAP). Analysis from an observational, multicentre cohort study initiated by the German competence network for CAP was performed. Patients were analysed separately as an influenza season and off-season cohort. Associations between vaccination status and outcome parameters were evaluated by multivariate analyses. In the season cohort (2,368 patients) CAP in vaccinated patients was significantly less severe according to most analysed parameters (CURB index ≥ 1: OR 0.76, 95% CI 0.60-0.98; procalcitonin ≥ 2.0 ng·mL(-1): OR 0.53, 95% CI 0.35-0.81; procalcitonin ≥ 0.5 ng·mL(-1): OR 0.71, 95% CI 0.51-0.99) and these patients showed a significantly better overall survival within the 6-month follow-up period (HR 0.63, 95% CI 0.45-0.89). Within the off-season cohort (2,632 patients) there was no significant influence of vaccination status on CAP severity or disease outcome. In conclusion, prior influenza vaccination was associated with less severe clinical course and improved overall long-term survival in patients with CAP during influenza seasons.