Does Flu Vaccination Lower Risk for Pneumonia in Elders?

Previous observational studies have shown that influenza vaccination lowers risk for pneumonia in older patients. In a population-based case-control study, conducted during the preinfluenza and influenza seasons of 2000, 2001, and 2002, Seattle investigators studied managed-care records for 1173 older patients (age range, 65–94) with community-acquired pneumonia (CAP) and for 2346 age- and sex-matched controls without CAP. Both groups were equally likely to have been vaccinated (roughly 60% before the CAP index date and 77% by the end of each influenza season).

In unadjusted analyses, vaccinated patients had a 40% lower risk for CAP than unvaccinated patients in the preinfluenza period — when no biologically plausible explanation exists for …