Consistent evidence from more than 40 studies shows that seasonal influenza can trigger acute myocardial infarction and cardiovascular death.
The review also found “some evidence that influenza vaccines are effective at reducing the risk of cardiac events in those patients with established cardiovascular disease,” said Dr. Charlotte Warren-Gash of the Centre for Infectious Disease Epidemiology at the Royal Free Hospital in London and her associates (Lancet Infect. Dis. 2009;9:601-9).
A large body of published work suggests that a range of acute and chronic bacterial and viral infections might be associated with an increased risk of acute MI. Influenza, however, stands out because of its substantial clinical and public health effects, the authors wrote.
Influenza might acutely stimulate inflammation or coagulation. The virus may also affect endothelial function or stimulate coronary artery remodeling.
Their research identified 42 studies published between 1932 and 2008 that examined the outcomes of MI or death from cardiovascular disease in patients infected with influenza or an acute respiratory infection or in people who received influenza immunization. They included 12 case-control studies that looked for associations between acute MI and either presumed influenza infection or nonspecific respiratory infection. Four other case-control studies examined links between flu immunization and acute MI or cardiovascular disease death.
The review also included two intervention studies that tested whether flu immunization prevented MI or cardiovascular death. The two intervention studies were relatively small, involving a total of just under 1,000 patients. The meta-analysis showed a statistically significant 61% reduction in cardiovascular deaths with influenza immunization, compared with no immunization, but the analysis also showed no significant effect of immunization on the MI rate.
The authors said that they had no conflicts of interest.