Among non-traditional cardiovascular (CV) risk factors, recent acute respiratory infection is strongly associated with acute atherothrombotic events. Given a possible mechanism of destablization of atherosclerotic plaque or compromise of a vulnerable CV patient, influenza vaccine is a potential therapy that may reduce CV events with one simple yearly inoculation.
We performed a systematic review and meta-analysis of randomized controlled trials (RCTs) that studied influenza vaccine versus control in patients with and without established cardiovascular disease (CVD). Random effects models with summary Mantel-Haenszel (M-H) odds ratios (OR) and 95% confidence intervals (CI) for major adverse CV events (MACE), CV death, and all-cause mortality were constructed.
Four RCTs of moderate quality conducted between 1994-2008 met inclusion criteria. In total, 3,227 patients were enrolled; 796 were early post-acute coronary syndrome, 851 had stable CVD, and 1,580 were without established CVD. A total of 187 MACE events, including 65 CV deaths, and 70 total deaths occurred after a median of 1 year of follow-up. Influenza vaccine significantly reduced the 1-year risk of MACE (M-H OR 0.52, 95% CI 0.37-0.74; p=0.0002) with a directionally consistent trend for CV death (M-H OR 0.58, 95% CI 0.25-1.36; p=0.21) and all-cause mortality (M-H OR 0.63, 95% CI 0.29-1.35; p=0.23; Figure 1
). There was no significant heterogeneity between studies (p>0.10).
Influenza vaccine reduced non-fatal CV events and may reduce sudden CV death in patients with and without CVD. However, the very low number of observed CV events and important design limitations among these RCTs strongly limit their validity and make it challenging to draw a definitive conclusion. A large, adequately powered, international multicenter RCT testing the efficacy of influenza vaccine to reduce incident and recurrent CV events is prudent to confirm these findings.
© 2012 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.