Impact of Statins on Influenza Vaccine Effectiveness Against Medically Attended Acute Respiratory Illness

Background. Statins have antiinflammatory effects that may impact vaccine-induced immune responses. We investigated the impact of statin therapy on influenza vaccine effectiveness (VE) against medically attended acute respiratory illness (MAARI). Methods. We conducted a retrospective cohort study over nine influenza seasons using research databases of a large managed care organization in the United States. Influenza vaccination and statin prescription statuses of cohort members and MAARI cases were ascertained on a per-season basis. Incidence rate ratios (IRRs) of MAARI were estimated using Poisson regression and stratified by statin use. Using a ratio of ratios approach, we compared IRRs from periods during to IRRs from periods before influenza circulation and then used relative IRRs to compute VE. Results. After adjustment for multiple prespecified covariates, the influenza VE against MAARI was lower among statin users than nonusers during periods of local (14.1% vs 22.9%; mean difference, 11.4%; 95% confidence interval [CI], -1.7% to 26.1%) and widespread (12.6% vs 26.2%; mean difference, 18.4%; 95% CI, 2.9%-36.2%) influenza circulation. Conclusions. In this study, statin therapy was associated with reduced influenza VE against MAARI. Since many cases of MAARI are not caused by influenza, studies of the impact of statins on influenza VE against laboratory-confirmed influenza are needed.