Importance of attributable risk in monitoring adverse events after immunization: Hepatitis B vaccination in children

Objectives. Most vaccine safety data present only the postvaccination incid ence of all adverse events rather than an estimate of attributable risk. Th is study sought to illustrate the difference between the 2 estimates with d ata from a hepatitis B immunization program. Methods. The incidence of health problems occurring before and after each d ose of hepatitis B vaccine in a cohort of 1130 children were compared. Results. Although 47.5% of all children reported an adverse event during th e following each of the 3 doses, attributable to immunization occurred in o nly 10.6% of children. Conclusions. Postimmunization incidence systematically overestimates the ri sk of adverse events. Estimating actual attributable risk is necessary to a void false beliefs regarding immunization.