Association between Influenza Vaccination and Adverse Cardiovascular Outcomes in the Active Component, U.S. Armed Forces, 2008-2013

Background: Influenza epidemics cause significant influenza-associated hospitalizations and deaths. Cardiovascular disease is a comorbidity that increases risk of influenza-related complications. Observational studies detected an increase in cardiovascular deaths during increased influenza activity. Recent studies suggest influenza vaccine is protective against cardiovascular events, even though no such studies were conducted in the U.S. military population. Service members are required to receive annual influenza vaccinations, yet the vaccination rate is less than 100 percent suggesting that unvaccinated individuals with cardiac risk factors may be at greater risk for adverse cardiac outcomes. As a result, this presentation will investigate the association between influenza vacciantion and adverse cardiac outcomes. 

METHODS: This retrospective cohort study utilized ICD-9-CM-based medical encounters in the Defense Medical Surveillance System (DMSS). The study population consisted of active component, U.S. Armed Forces service members (Army, Navy, Air Force, Marines, Coast Guard), 30 years and older. The surveillance period was 2008-2013 and included the five influenza seasons. The outcome, major adverse cardiac event (MACE), was defined as an inpatient encounter of MI, angina, heart failure, stroke, or other chronic ischemic heart disease. Multivariate logistic regression was used to assess the effect of influenza vaccination status and other covariates on MACE outcome. 

RESULTS: Overall, incidence of MACE was less than 1%, but higher in service members not vaccinated. All five influenza seasons showed a statistically significant protective association between influenza vaccination and MACE outcome. After adjusting for age, race/ethnicity, history of smoking, diabetes, hypertension, hyperlipidemia, and AFIB, the RR among those with influenza vaccination compared to those without ranged from 0.27 (95% CI: 0.21, 0.34) in season 2009-2012, to 0.55 (95% CI: 0.45, 0.67) in season 2011-2012.  

CONCLUSIONS: Influenza vacciantion was associated with a lower risk for MACE in service members 30 years and older in the active component, U.S. Armed Forces. This suggests that further education to medical personnel about potential benefits of influenza vaccine on cardiac outcomes is warranted in an effort to achieve full compliance with DoD vaccination requirements. Additionally, primary care and cardiology clinics should make influenza vaccines available to improve vaccination rates among those with cardiac risk factors.