Influenza vaccination and risk of community-acquired pneumonia

Lancet Volume 372, Issue 9636, 2 August 2008-8 August 2008, Pages 398-405 Pneumonia is a common complication of influenza infection in elderly individuals and could therefore potentially be prevented by influenza vaccination. In studies with data from administrative sources, vaccinated elderly people had a reduced risk of admission for pneumonia compared with unvaccinated seniors; however, these findings could have been biased by underlying differences in health between the groups. Furthermore, since most individuals with pneumonia are not treated in hospital, such studies should include both outpatient and inpatient events. We therefore assessed whether influenza vaccination is associated with a reduced risk of community-acquired pneumonia in immunocompetent elderly people after controlling for health status indicators.

Findings 1173 cases and 2346 controls were included in the study. After we adjusted for the presence and severity of comorbidities, as defined by chart review, influenza vaccination was not associated with a reduced risk of community-acquired pneumonia (odds ratio 0·92, 95% CI 0·77–1·10) during the influenza season.

Interpretation The effect of influenza vaccination on the risk of pneumonia in elderly people during influenza seasons might be less than previously estimated.