Influenza and Pneumococcal Vaccinations Fail to Prevent Myocardial Infarction

Background: Four observational studies and one clinical trial have suggested that influenza vaccination is associated with a >50% reduction in risk of cardiac sudden death, myocardial infarction (MI), and stroke. One observational study found no effect. Objective: To identify an association between influenza or pneumococcal vaccination and myocardial infarction. Methods: We conducted a case-control study of discharges from nine metropolitan hospitals to identify a possible association between both influenza and pneumococcal vaccinations and MI, using patients with bone fractures as controls. We administered a standardized questionnaire to 335 MI patients and 199 patients with fractures (76% of eligible patients). Results: The groups significantly differed by sex, age, body mass index, smoking status, family history of heart disease, personal history of cardiovascular disease, and number of self-reported upper respiratory infections both during the winter months of interest and in the two weeks prior to their index event. Influenza vaccine had been administered to 177 (53%) MI patients and 126 (63%) fracture patients (p = 0.049) with an adjusted odds ratio (OR) = 0.90 (95% confidence interval 0.60, 1.35), p = 0.593. In 148 pairs matched by age and sex, the post hoc adjusted OR = 0.97. Pneumococcal vaccine had been administered to 107 (32%) MI patients and 78 (39%) fracture patients (p = 0.203) with an adjusted OR = 0.89 (95% confidence interval 0.60, 1.33), p = 0.577, and a power = 0.96 to detect a difference ≧40%. Conclusions: Neither influenza nor pneumococcal vaccine is associated with a reduced risk of myocardial infarction. A randomized controlled trial is needed.