Influenza Vaccination and Major Adverse Vascular Events in High Risk Patients
Background—We sought to determine the association between influenza vaccination and major adverse vascular events, as the association remains uncertain.
Methods and Results—31,546 participants were enrolled from 40 countries. Eligibility included age ≥55 years and known vascular disease. The primary outcome was a composite of death from cardiovascular causes, myocardial infarction, or stroke during 4 influenza seasons (2003-2007). Influenza vaccination was associated with a lower risk of the outcome during three influenza seasons (defined using WHO FluNet reports); 2004-2005 (adjusted OR (aOR) 0.62 [95% CI 0.50-0.77]), 2005-2006 (aOR 0.69 [95% CI 0.53-0.91]) and 2006-2007 (aOR 0.52 [95% CI 0.42-0.65]); the same years circulating influenza matched the vaccine antigen. In 2003-2004, there was an incomplete match between circulating influenza and the vaccine antigen and there was no association between influenza vaccination and the outcome (aOR 0.96 [95% CI 0.73-1.27]). However, tests of potential biases in the analyses revealed associations between influenza vaccination and the outcome during non-influenza seasons except 2003-2004. Summary OR in the influenza season (OR 0.65 [95% CI 0.58-0.74]) and non-influenza season (OR 0.66 [95% CI 0.57-0.76]) were almost identical. Reduction in risk of non-cardiovascular death associated with the influenza vaccine ranged from 73% to 79%.
Conclusions—Although initial analyses suggest that influenza vaccination was associated with reduced risk of major adverse vascular events during influenza seasons when the influenza vaccine matched the circulating virus, sensitivity analyses revealed that risk of bias remained. A randomized trial is needed to definitively address this question.
- Received September 29, 2011.
- Accepted May 16, 2012.
- Copyright © 2012, American Heart Association, Inc. All rights reserved. Unauthorized use prohibited