Clinical Question

Does the influenza vaccine lower the risk of major adverse cardiovascular events in adults with coronary disease?

Bottom Line

This meta-analysis found that the influenza vaccine is associated with a significantly lower risk of major adverse cardiovascular events in adults with coronary disease. The benefit of influenza vaccination is strongest in adults with a history of recent acute coronary syndrome within the previous six months (number needed to treat [NNT] = 8). (Level of Evidence = 1a)

Synopsis

These investigators searched multiple sources, including Medline, Embase, the Cochrane Register, reference lists of eligible articles, clinicaltrials.gov, and conference abstracts without language restrictions for all published and unpublished randomized clinical trials comparing influenza vaccination with placebo or standard care. Two investigators independently reviewed potential studies for inclusion and methodologic quality using standard scoring tools. Disagreements were resolved by consensus. Six randomized controlled trials met inclusion criteria for the final meta-analysis. These trials (N = 6,735) compared influenza vaccine with placebo or control for a mean duration of 7.9 months. The primary outcome measured was a composite of major adverse cardiovascular events, including cardiovascular death or hospitalization for myocardial infarction, unstable angina, stroke, heart failure, or urgent coronary bypass surgery.

In the analysis of the six included trials, significantly fewer vaccinated patients developed a major adverse cardiovascular event compared with those in the placebo or control groups (2.9% vs. 4.7%, respectively; NNT = 58; 95% confidence interval, 38 to 124). The benefit of vaccination was strongest in the subset of patients with a history of recent acute coronary syndrome within the previous six months (10.25% with vaccine vs. 23.1% with placebo or control; NNT = 8; 95% confidence interval, 6 to 13). There was, however, no significant difference in all-cause mortality between the vaccinated and placebo or control patient groups. Formal statistical analyses found no evidence of significant heterogeneity among the trials or publication bias.

Study design: Meta-analysis (randomized controlled trials)

Funding source: Government

Setting: Various (meta-analysis)

Reference: UdellJAZawiRBhattDLet alAssociation between influenza vaccination and cardiovascular outcomes in high-risk patients: a meta-analysis. JAMA. 2013; 310( 16): 1711– 1720.