Influenza and complications associated with influenza including pneumonia impose a significant burden on the healthcare system, particularly in elderly individuals. Although the influenza vaccine could potentially reduce the risk of complications, its benefit in this group remains doubtful.

This population-based nested case-control study investigated whether the influenza vaccine reduced the risk of community acquired pneumonia in immunocompetent elderly individuals. The cohort comprised people aged 65–94 years who had enrolled in a health maintenance organisation in Washington State during the pre-influenza and influenza seasons in 2000, 2001 and 2002.

A total of 1173 individuals with pneumonia confirmed by medical records or chest radiography were included (714 of whom had been vaccinated against influenza). 2346 individuals without pneumonia (two age- and sex-matched for each case) served as controls (1838 of whom had not received the influenza vaccination). The presence of heart and lung diseases, frailty indicators, smoking history, use of respiratory medications and routine prescriptions were reviewed and adjusted to reduce confounding factors. After adjustment, influenza vaccination was not associated with a reduction in community acquired pneumonia during the influenza season. The authors suggested two potential explanations; either influenza caused a small proportion of pneumonia in elderly people or the available vaccine was less effective in reducing the risk of pneumonia.

Although this was a large population-based study and raises important questions, more robust randomised controlled trials are needed to determine the effectiveness of the influenza vaccine in reducing influenza-related morbidity in this age group. Until this happens, the influenza vaccination will continue to be used as a health protective measure worldwide.

▸ Jackson ML, Nelson JC, Weiss NS, et al. Influenza vaccination and risk of community-acquired pneumonia in immunocompetent elderly people: a population-based, nested case-control study. Lancet 2008;372:398–405.