Association of influenza vaccination and reduced risk of recurrent myocardial infarction

Background-Numerous studies have suggested that microbial agents may promot e atherosclerosis. A smaller body of research has suggested that acute resp iratory infection may be a risk factor for myocardial infarction (MI). We h ypothesized that influenza vaccine might reduce the risk of recurrent MI in patients with documented coronary heart disease (CHD). Methods and Results-A case-control study was performed on 218 CHD patients seen at Memorial Hermann Hospital during the influenza season of October 19 97 through March 1998. Patients who experienced new MI were included in the case group, and those who did not experience new MI or unstable angina wer e assigned to the control group. Data were collected by structured review o f patients' charts and through a subsequent telephone survey. Adjusted for history of influenza vaccination in previous years, multivariate logistic r egression revealed risk of MI to be associated with current hypertension (O R 4.96, 95% CI 2.06 to 11.96, P<0.0001), hypercholesterolemia (OR 4.08, 95% CI 1.67 to 9.99, P=0.002), smoking (OR 3.75, 95% CI 1.76 to 7.98, P=0.001) , and influenza vaccination (OR 0.33, 95% CI 0.13 to 0.82, P=0.017). Despit e significant association in univariate analysis, multivitamin therapy and physical exercise were not associated with risk of reinfarction in multivar iate analysis. Conclusions-In this study in patients with chronic CHD, vaccination against influenza was negatively associated with the development of new MI during the same influenza season. However, to address causal inference, examinatio n of prospective data sets will be needed.