Evaluating the impact of statin use on influenza vaccine effectiveness and influenza infection in older adults

Abstract Background Older adults are recommended to receive influenza vaccination annually and many use statins. Statins have immunomodulatory properties that might modify influenza vaccine effectiveness (VE) and alter influenza infection risk. Methods Using the test-negative design and linked laboratory and health administrative databases in Ontario, Canada, we estimated VE against laboratory-confirmed influenza among community-dwelling statin users and non-users aged ≥66 years during the 2010-2011 to 2018-2019 influenza seasons. We also estimated the odds ratio (OR) for influenza infection between statin users and non-users by vaccination status. Results Among subjects tested for influenza across the 9 seasons, 54,243 had continuous statin exposure prior to testing and 48,469 were deemed unexposed. VE against laboratory-confirmed influenza was similar between statin users and non-users (17% [95%CI, 13-20%] and 17% [95%CI, 13-21%] respectively; test for interaction, p=0.87). In both vaccinated and unvaccinated subjects, statin users had higher odds of laboratory-confirmed influenza than non-users (OR for vaccinated =1.15; 95%CI, 1.10-1.21; OR for unvaccinated=1.15; 95%CI, 1.10-1.20). These findings were consistent by mean daily dose and statin type. VE did not differ between users and non-users of other cardiovascular drugs, except for beta-blockers. We did not observe that vaccinated and unvaccinated users of these drugs had increased odds of influenza, except for unvaccinated beta-blocker users. Conclusions Influenza VE did not differ between statin users and non-users. Statin use was associated with increased odds of laboratory-confirmed influenza in vaccinated and unvaccinated subjects, but these associations might be impacted by residual confounding.