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

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.