Influenza vaccination reduces hospitalization for acute coronary syndrome in elderly patients with chronic obstructive pulmonary disease: A population-based cohort study

Elderly patients with chronic obstructive pulmonary disease (COPD) are at a higher risk of hospitalization for cardiovascular complications, especially during respiratory infections. Previous studies showed that vaccination for influenza may reduce the risk of recurrent major cardiovascular events in patients with acute coronary syndrome (ACS). The purpose of this study was to evaluate the hypothesis that influenza vaccination could reduce hospitalizations for ACS in elderly patients with COPD.Using the Taiwan Longitudinal Health Insurance Database 1996–2008, this cohort study comprised elderly patients (≥55 years old) with a recorded diagnosis of COPD (n=7722) between January 1, 2000 and December 31, 2007. Each patient was followed until the end of 2007. A propensity score was derived by using a logistic regression model to reduce vaccine therapy selection bias. The hazard ratio (HR) and 95% confidence interval (CI) for the association between the influenza vaccination and the occurrence of first hospitalization for ACS in elderly COPD patients was examined by Cox proportional hazards regression analysis. In addition, we categorized the patients into four groups according to vaccination status (unvaccinated, total number of vaccinations: 1, 2−3, and ≥4).We found that elderly patients with COPD receiving influenza vaccination had a lower risk of hospitalization for ACS (adjusted HR=0.46, 95% CI (0.39–0.55), p<0.001). We observed similar protective effects in both sexes and all age groups (55−64, 65−74, ≥75) regardless of influenza seasonality. When the patients were stratified according to the total number of vaccinations, the adjusted HRs for hospitalization because of ACS were 0.48 (0.38−0.62) and 0.20 (0.14−0.28) for patients who received 2−3 and ≥4 vaccinations during the follow-up period.Our data showed that there was a lower risk of ACS hospitalization in elderly patients with COPD receiving annual influenza vaccination.