Influenza vaccine associated with lower risk of major cardiovascular events

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1. Influenza vaccination is associated with lower risk of major adverse cardiovascular events within one year. 

2. Patients with acute coronary syndrome substantially benefit from lower rates of adverse cardiovascular events compared to those with stable coronary artery disease. 

Evidence Rating Level: 1 (Excellent)       

Study Rundown: Each year, influenza is a significant cause of morbidity and mortality in the United States, especially among people with underlying high-risk conditions. Guidelines that recommend patients with cardiovascular disease receive influenza vaccinations are largely based on observational findings. In this meta-analysis, a systematic review of randomized controlled trials (RCTs) was conducted to determine if vaccination decreased the risk of major adverse cardiovascular events. In 6 RCTs, with 6735 subjects, 2.9% of patients who were vaccinated developed adverse cardiovascular events, compared to 4.7% of patients without vaccination (P = .003). Furthermore, in patients with a recent history of acute coronary syndrome, vaccination was associated with lower risk of adverse events (10.25% influenza vaccine vs. 23.1% placebo or control (P < .001) compared to patients with stable coronary artery disease (6.9% influenza vaccine vs. 7.4% placebo or control (P = .81). Strengths of the study include drawing from large biomedical databases, selection of unbiased RCTs, and few inconsistencies between chosen trials. Limitations include a variety of severe and less severe endpoints for cardiovascular adverse events, and heterogeneity between primary and secondary endpoints and prevention populations. The study influences clinical practice by providing evidence supporting vaccinations of all patients with underlying cardiovascular disease in order to prevent adverse events.

Click to read the study published today in JAMA

Click to read an accompanying editorial published today in JAMA

Relevant Reading: Risk of Myocardial Infarction and Stroke after Acute Infection or Vaccination

In-Depth [meta-analysis]: In this study included 12 RCTs that were included in the final meta-analysis: 6 studies (5 published, 1 unpublished) with vaccination vs. placebo (primary analysis), and 6 studies with experimental vs. standard vaccination (secondary analysis). Cardiovascular outcomes (myocardial infarction, angina, stroke, heart failure, revascularization, or cardiovascular death) were either primary (efficacy) or secondary (safety) endpoints in these studies. In studies comparing vaccination vs. placebo, 2.9% developed adverse cardiovascular events compared to 4.7% treated with placebo or control in one-year follow-up  (RR, 0.64 [95% CI, 0.48-0.86], P = .003), with absolute risk difference of 1.74% (95% CI, 0.81%-2.67%; P = .003) or an NNT of 58 (95% CI, 38-124) to prevent one major adverse cardiovascular event. Patients with recent acute coronary disease had lower risk of major events (10.25% influenza vaccine vs. 23.1% placebo or control; RR, 0.45 [95% CI, 0.32-0.63]; P < .001) compared to patients with stable coronary artery disease (6.9% influenza vaccine vs. 7.4% placebo or control; RR, 0.94 [95% CI, 0.55-1.61]; P = .81).

By Gayatri Boddupalli and Brittany Hasty 

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