Given that previous research has shown a link between influenza infection and increased risk of negative cardiovascular outcomes, a new review published in the Cochrane Library looks to assess the possible benefits of influenza vaccination on cardiovascular disease prevention. Previous studies have demonstrated a link between influenza vaccination and reduced all-cause mortality, heart attack and stroke, but these studies were observational in nature and the results were likely prone to bias.
In this updated review, researchers included six new clinical trials, in addition to the two trials used in the previous review. The eight trials were divided into two groups and analysed separately, with four trials focusing on prevention of influenza in the general or elderly population and reported cardiovascular outcomes, and another four focusing on prevention of cardiovascular events in coronary heart disease (CHD) patients. Follow-up was between 42 days and one year.
Cardiovascular mortality was found to be significantly reduced by influenza vaccination in four, secondary prevention trials (risk ratio 0.45) with no significant heterogeneity between studies. While the number of cardiovascular events was too small to permit conclusions, three trials that included cardiovascular mortality as part of the safety analyses found no difference between study groups. In patients with CHD, the studies showed a decrease in composite outcomes of cardiovascular events with influenza vaccination vs. placebo. With regards to individual outcomes such as myocardial infarction, no significant difference was seen between the comparison groups.
The authors conclude that the studies used for this review did not provide enough evidence to prove that influenza vaccination is beneficial in primary prevention of cardiovascular death or non-fatal cardiovascular events. Influenza vaccination may reduce cardiovascular events and death in patients with established cardiovascular disease, but the evidence is limited. Future studies must be adequately powered to measure these outcomes and should also include patients with cardiovascular risk factors, not just those with established cardiovascular disease.