Does Flu Vaccination Lower Risk for Pneumonia in Elders?

In contrast to results of previous studies, flu vaccine did not lower risk in this study. 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 vaccine benefit — but the difference disappeared when analyses were adjusted for a wide range of chronic diseases and functional impairment. No difference in risk for CAP was observed between vaccinated and unvaccinated groups during the influenza season, whether analyses were adjusted or not, and no difference was observed in risk for CAP that required hospital admission during peak influenza season.

Comment:

According to this provocative study, influenza vaccination offered no benefit in broad measures of risk for community-acquired pneumonia. Editorialists noted that this study has several strengths that have been missing in many other studies: It was conducted during seasons when the antigenic match between influenza strains and vaccine was good; CAP was ascertained with chart audit rather than by evaluating administrative data; the analysis was controlled for a wide range of chronic disease and functional status measures; and both inpatient and outpatient cases were identified.

-Thomas Schwenk, M.D.