Statin use and risks of influenza-related outcomes among older adults receiving standard-dose or high-dose influenza vaccines through Medicare during 2010-2015.

Background. Stalins are used to reduce cardiovascular disease risk. Recent studies suggest that stalin use may be associated with an increased influenza risk among influenza vaccinees. We used Medicare data to evaluate associations between stalins and risks of influenza-related encounters among vaccinees. Methods. In this retrospective cohort study, we identified Medicare beneficiaries aged > 65 years who received high-dose (HD) or slandard-dose (SD) influenza vaccines at pharmacies from 2010-2011 through 2014-2015. Statin users were matched to nonusers by vaccine type, demographics, prior medical encounters, and comorbidities. We used multivariable Poisson models to estimate associations between statin use around the time of vaccination and risk of influenza-related encounters. Study outcomes included influenza-related office visits with a rapid test followed by dispensing of oseltamivir and influenza-related hospitalizations (including emergency room visits) during high influenza circulation periods. Results. The study included 1403 651 statin users matched to nonusers. Cohorts were well balanced, with standardized mean differences <0.03 for all measured covariates. For stalin users compared to nonusers, the adjusted relative risk was 1.086 (95% confidence interval [CI], 1.025-1.150) for influenza-related visits and 1.096 (95% CI, 1.013-1.185) for influenza-related hospitalizations. The risk difference ranged from -0.02 to 0.23 for influenza-related visits and from -0.04 lo 0.13 for hospitalizations, depending on season severity. Results were similar for HD and SD vaccinees and for nonsynlhetic and synthetic statin users. Conclusions. Among 2.8 million Medicare beneficiaries, these results suggest that statin use around the time of vaccination does not substantially affect the risk of influenza-related medical encounters among older adults.