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

ABSTRACT

OBJECTIVES: Most vaccine safety data present only the postvaccination incidence of all adverse events rather than an estimate of attributable risk. This study sought to illustrate the difference between the 2 estimates with data from a hepatitis B immunization program. METHODS: The incidence of health problems occurring before and after each dose of hepatitis B vaccine in a cohort of 1130 children were compared. RESULTS: Although 47.5% of all children reported an adverse event during the 4 weeks following each of the 3 doses, adverse events attributable to immunization occurred in only 10.6% of children. CONCLUSIONS: Postimmunization incidence systematically overestimates the risk of adverse events. Estimating actual attributable risk is necessary to avoid false beliefs regarding immunization.