Influenza vaccination should be encouraged whenever it is indicated, particularly in people with cardiovascular disease—a group in which the shots appear to be underutilized.

Researchers reviewed evidence that flu (including flulike illness and acute respiratory infection) triggers heart attacks or cardiovascular deaths (Lancet Infect Dis. 2009; 9:601-610). A protective, though nonsignificant, effect of vaccination for heart patients was found.

The investigative team analyzed 42 papers describing 39 studies conducted between 1932 and 2008. Almost all focused on seasonal influenza. Although findings varied substantially from study to study (partly because of changing case definitions and differential influenza circulation over the years), researchers found that even the lowest reported numbers for excess deaths due to cardiovascular disease were large.

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“A range of observational studies done in different settings have generally tended to support the hypothesis that acute respiratory infections—influenza in particular—can trigger acute MI,” the authors conclude. “There is also more limited evidence for an adverse effect on cardiovascular death. Two relatively small randomized trials [included in the analysis] suggest that influenza vaccination reduces the risk of cardiovascular death and some coronary ischemic events.”

The investigators contend that their findings highlight the need to encourage vaccination for all indicated patients. Influenza is one of the most common respiratory infections and the only major respiratory virus for which effective preventive vaccination is available.