Repeated Annual Seasonal Influenza Vaccination of Patients With Circulatory Disease as Secondary Prevention of Cardiovascular Events: an Additional Self-Controlled Case Series Analysis.

Aim     To assess the effect of annual seasonal flu vaccination for 3 years on the risk of acute respiratory infection (ARI) and cardiovascular events (CVE) in cardiological patients followed up using two analytical methods.Material and methods            This prospective comparative study included 817 patients in October 2012. CVE, other chronic non-communicable diseases, and ARI recorded from October 2012 through November 2015 were analyzed. Vaccinated and unvaccinated patients were compared using survival curves and a self-controlled case series method for paired 6-month periods. Differences were considered statistically significant at p<0.05.Results            The analysis included 813 patients (mean age, 63.3±11.6 years; 40.5% men; in the 2012/13-2013/14-2014/15 season, 45-44-41% of patients, respectively, were vaccinated; 1, 2, and 3 vaccinations were received by 60, 57, and 285 patients, respectively; 413 were unvaccinated). Compared to unvaccinated patients, the patients vaccinated three times developed the first ARI later (p<0.0001); the relative risk of developing cardiovascular complications (CVC) was 0.88 (95% confidence interval: 0.65-1.10). Among vaccinated patients, there were fewer patients with ARI (p<0.001) and cardiovascular diseases (p=0.02) not only in summer compared to winter, but also in summer, ARI developed in 41.2% fewer patients than in unvaccinated (p=0.002).Conclusion      The use of two analytical methods allowed us to identify additionally both non-specific and persistent specific effects of three-year flu immunization in cardiological patients in summer, which needs to be confirmed in randomized placebo-controlled studies.