During the 4.5-year study period , 60 cases of hepatitis E were identified ; 7 cases were confirmed in the vaccine group ( 0.3 cases per 10,000 person-years ) , and 53 cases in the control group ( 2.1 cases per 10,000 person-years ) , representing a vaccine efficacy of 86.8 % ( 95 % confidence interval , 71 to 94 ) in the modified intention-to-treat analysis , rather than ( 95 % confidence interval , 71 to 84 ) [ corrected ] .