Flu vaccine lowers risk for cardiac events

HealthDay News -- Influenza vaccination is associated with a lower risk of cardiovascular events among those at high risk of cardiovascular disease, particularly among those with more active coronary disease, results of a meta-analysis show.

Pooled results from five randomized trials indicate the event rate was 2.9% among those who received the flu vaccine and 4.7% among those who did not (risk ratio 0.64, 95% CI 0.48-0.86), Jacob A. Udell, MD, MPH, from the University of Toronto, and colleagues reported in Journal of the American Medical Association.

The benefit was even greater among those with a history of acute coronary syndrome (ACS) in the year prior to randomization(RR 0.45, 95% CI 0.32-0.63), they found.

"Influenza vaccination may prevent cardiovascular events via avoidance of atherosclerotic plaque rupture or other forms of cardiac injury in a vulnerable patient and represents a simple, once-annual protective therapy to reduce cardiovascular events," the researchers explained.

Influenza is consider a risk factor for atherothrombotic events and results from previous studies have found associations between flu vaccination and reduced cardiovascular events. To explore the issue further, Udell and colleagues performed a metanalysis of five published trials and one unpublished trial that involved 6,735 patients at high risk of cardiovascular disease and compared influenza vaccination versus placebo or control.

Average patient age was 67 years, and mean follow-up time was 7.9 months. More than one third of patients had a history of heart disease (36.2%).

The primary endpoint was a composite of cardiovascular death or hospitalization for heart failure, myocardial infarction, unstable angina, stroke or urgent coronary revascularization. 

The researchers found that influenza vaccination was associated with a significantly lower risk of composite cardiovascular events (2.9% vs. 4.7%; relative risk 0.64) with a number needed to treat (NNT) of 58. The lower risk was largely confined to patients with a recent history of acute coronary syndrome (within one year of randomization; relative risk, 0.45; P< 0.001) compared to those without a recent history of acute coronary syndrome (relative risk, 0.94; P=0.81). The NNT in the ACS group was eight.

"This finding has considerable clinical and health policy importance, given the profound under-use of vaccination among the general public and the potential impact this preventive strategy may have on high-risk patients," the researchers wrote.

In an accompanying editorial, Kathleen Neuzil, MD, MPH, of PATH in Seattle, warned that the findings are "limited by the quality of the underlying studies and do not imply causation." However, she added, "regardless of whether influenza vaccine reduces cardiovascular disease, the known morbidity of influenza in older adults with and without high-risk conditions [...] warrant its use."

Limitations of the meta-analysis include the relatively small number of cardiovascular events, between study differences in patient populations and primary outcomes and various methodological flaws. 

References

  1. Udell J et al. JAMA. 2013; 310: 1711-1720.
  2. Neuzil K. JAMA. 2013; 310: 1681-1682.
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