Effect of age on relative effectiveness of high-dose versus standard-dose influenza vaccines among US Medicare beneficiaries ages 65 years and older

Background. Studies have found that the high-dose influenza vaccine has a higher relative vaccine effectiveness (RVE) versus standard-dose vaccines in some seasons. We evaluated the effect of age on the RVE of high-dose versus standard-dose influenza vaccines among Medicare beneficiaries. Methods. A 6-season retrospective cohort study from 2012 to 2018 among Medicare beneficiaries aged =65 years was performed. Poisson regression was used to evaluate the effect of age on the RVE of high-dose versus standard-dose influenza vaccines in preventing influenza-related hospitalizations. Results. The study included >19 million vaccinated beneficiaries in a community pharmacy setting. The Poisson models indicated a slightly increasing trend in RVE with age in all seasons. The high-dose vaccine was more effective than standard-dose vaccines in preventing influenza-related hospital encounters (ie, influenza-related inpatient stays and emergency department visits) in the 2012-2013 (RVE, 23.1%; 95% confidence interval [CI], 17.6%-28.3%), 2013-2014 (RVE, 15.3%; 95% CI, 7.8%-22.3%), 20142015 (RVE, 8.9%; 95% CI, 5.6%-12.1%), and 2016-2017 (RVE, 12.6%; 95% CI, 6.3%-18.4%) seasons and was at least as effective in all other seasons. We also found that the high-dose vaccine was consistently more effective than standard-dose vaccines across all seasons for people aged >= 85 years. Similar trends were observed for influenza-related inpatient stays. Conclusions. The RVE of high-dose versus standard-dose influenza vaccines increases with age.