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.