Association of influenza vaccination with reduced risk of venous thromboembolism.

Influenza vaccination can reduce the risk of cardiovascular events in patients with coronary heart disease, but its impact on the risk of venous thromboembolism (VTE) has not been studied. It was the aim of this study to investigate whether influenza vaccination reduces the risk of VTE. We conducted a case-control study involving 1,454 adults enrolled in 11 French centers between 2003 and 2007, comprising 727 consecutive cases with a first documented episode of VTE and 727 age- and sex-matched controls. In the case and control groups 202 (28.2%) and 233 (32.1%) subjects, respectively, had been vaccinated against influenza during the previous 12 months. After multivariate regression analysis, the odds ratios (OR) for VTE associated with vaccination were 0.74 (95% confidence interval [CI], 0.57-0.97) and 0.52 (95% CI, 0.32-0.85), respectively, for the whole population and for subjects aged 52 years or less. The protective effect of vaccination was similar for deep venous thrombosis (OR 0.9, 95% CI, 0.60-1.35) and pulmonary embolism (OR 0.71, 95% CI, 0.53-0.94) and for both provoked (OR 0.71, 95% CI, 0.53-0.97) and unprovoked VTE (OR 0.85, 95% CI, 0.59-1.23). This case-control study suggests that influenza vaccination is associated with a reduced risk of VTE.