Receiving an influenza vaccination was associated with a lower risk of major adverse cardiovascular events such as heart failure or hospitalization for myocardial infarction, with the greatest treatment effect seen among patients with recent acute coronary syndrome, according to an analysis of previously published studies.
Among nontraditional cardiovascular risk factors, there remains interest in potential association between respiratory tract infections, of which influenza and influenza-like illnesses are common causes, and subsequent cardiovascular events, researchers wrote in background information for the article, which was published in the Oct. 23/30 issue of the Journal of the American Medical Association. Several epidemiological studies have suggested a strong inverse relationship between influenza vaccination and the risk of fatal and nonfatal cardiovascular events.
Jacob A. Udell, MD, MPH, FRCPC, of the University of Toronto, and colleagues conducted a meta-analysis of all randomized clinical trials of influenza vaccine that studied cardiovascular events as efficacy or safety outcomes. The researchers identified five published and one unpublished trials of 6,735 patients (average age 67, 51% women, 36% with a cardiac history, average follow-up time 7.9 months) that met inclusion criteria for the study. Analyses were stratified by subgroups of patients with and without a history of acute coronary syndrome within a year of randomization.
In the five published trials, 95 of 3,238 patients treated with influenza vaccine (2.9%) developed a major adverse cardiovascular event, compared with 151 of 3,231 patients (4.7%) treated with placebo or control within a year of follow-up, for an absolute risk difference favoring flu vaccine of 1.74%. The addition of the unpublished data did not materially change the results (2.9% influenza vaccine vs. 4.6% placebo or control).
In a subgroup analysis of three randomized controlled trials of patients with pre-existing coronary artery disease, the risk of major adverse cardiovascular events among patients with a history of recent acute coronary syndrome especially was lower with vaccine (10.3% influenza vaccine vs. 23.1% placebo or control), an absolute-risk difference of 12.9%. The difference was less significant in patients with stable CAD (6.9% influenza vaccine vs. 7.4% placebo or control). Results were similar with the addition of unpublished data.
Within this global meta-analysis of RCTs that studied patients with high cardiovascular risk, influenza vaccination was associated with a lower risk of major adverse cardiovascular events within one year, the researchers wrote. Influenza vaccination was particularly associated with cardiovascular prevention in patients with recent ACS.
Future research with an adequately powered multicenter trial to confirm the efficacy of this low-cost, annual, safe, easily administered and well-tolerated therapy to reduce cardiovascular risk beyond current therapies is warranted.