Estimated size of the population at risk of severe adverse events after smallpox vaccination in Israel

► The bioterror threat has prompted formulation of national preparedness strategies. ► We estimated the population at risk of adverse events of smallpox vaccine in Israel. ► The databases of the Israel Ministry of Health and the largest HMO were searched. ► This special population accounted for 4.3% of the national population. ► This information is essential for effective mass-vaccination programs.