Comparative effectiveness of high-dose versus standard-dose influenza vaccination in community-dwelling veterans.

BACKGROUND Influenza is a significant cause of morbidity and mortality in older adults. High-dose (HD) trivalent inactivated vaccine has increased immunogenicity in older adults compared with standard-dose (SD) vaccine. We assessed the relative effectiveness of HD influenza vaccination (vs SD influenza vaccination). METHODS We conducted a retrospective cohort study among patients who receive primary care at Veteran Health Administration (VHA) medical centers, and who received influenza vaccine in the 2010-2011 influenza season. The primary outcome was hospitalization for influenza or pneumonia. We also conducted an analysis in subgroups defined by age. RESULTS We evaluated 25 714 patients who received HD vaccine and 139 511 who received SD vaccine in 23 VHA medical centers. The rate of hospitalization for influenza or pneumonia was 0.3% in both groups in the influenza season. After accounting for patient characteristics in propensity-adjusted analyses, the risk of hospitalization for influenza or pneumonia was not significantly lower among patients receiving HD vaccine vs those receiving SD vaccine (risk ratio, 0.98; 95% confidence interval, .68-1.40). In the subgroup of patients ≥85 years of age, receiving HD (compared with SD) vaccine was associated with lower rates of hospitalization for influenza or pneumonia. CONCLUSIONS HD vaccine was not found to be more effective than SD vaccine in protecting against hospitalization for influenza or pneumonia; however, we found a protective effect in the oldest subgroup of patients. Additional studies are needed to evaluate the effectiveness of HD vaccine.