Rivaroxaban or Aspirin for Extended Treatment of Venous Thromboembolism | NEJMEfficacy Table 2. Prespecified Efficacy Outcomes. A primary efficacy outcome event occurred in 17 of 1107 patients (1.5%) who were receiving 20 mg of rivaroxaban and in 13 of 1127 patients (1.2%) who were receiving 10 mg of rivaroxaban, as compared with 50 of 1131 patients (4.4%) who were receiving aspirin. Fatal venous thromboembolism occurred in 2 patients (0.2%) who were receiving 20 mg of rivaroxaban, in no patients who were receiving 10 mg of rivaroxaban, and in 2 patients (0.2%) who were receiving aspirin (Table 2). Both rivaroxaban doses were superior to aspirin with respect to the primary efficacy outcome (hazard ratio for 20 mg of rivaroxaban vs. aspirin, 0.34; 95% confidence interval [CI], 0.20 to 0.59; hazard ratio for 10 mg of rivaroxaban vs. aspirin, 0.26; 95% CI, 0.14 to 0.47; P<0.001 for both comparisons). The hazard ratio for the comparison between the 20-mg and 10-mg rivaroxaban regimens was 1.34 (95% CI, 0.65 to 2.75; P=0.42). Similar results were found for the other efficacy outcomes (Table 2, and Table S4 in the Supplementary Appendix). Table 3. Rates of Recurrent Venous Thromboembolism and Major Bleeding, According to Risk Profile and Duration of Anticoagulation before Randomization. Figure 2. Kaplan–Meier Rates of Recurrent Fatal or Nonfatal Venous Thromboembolism and Major Bleeding. With aspirin, the rate of recurrent venous thromboembolism was 3.6% among the patients in whom the index event was provoked (i.e., associated with a known event, such as surgery or hospital admission) and 5.6% among those in whom the index event was unprovoked (i.e., idiopathic) (Table 3). Rates of recurrence in patients whose index events were provoked or unprovoked were lower in both the 20-mg rivaroxaban group (1.4% and 1.8%, respectively) and the 10-mg rivaroxaban group (0.9% and 1.5%, respectively) than in the aspirin group.