infection were 2.8%, 1.8%, and 0%, respec- tively, which represent 57% (2.8/4.9) of the headaches, 35% of the gastrointestinal prob- lems, and none of the respiratory tract infec- tions. Because the increased incidence occurred only during the first week, the absolute value of the attributable risk remains identical with longer follow-up (Table1), but the proportion of adverse events attributable to immunization decreases from 44% (10.6/24.2) during the first week to 22% (10.6/47.5) with a 4-week follow-up