Abstract
An unvaccinated boy, infected in his school, introduced variola minor (“alastrim”) in his household. All 3 exposed unvaccinated household members as well as 6 of the 13 exposed vaccinated persons developed variola in the first generation of subsequent cases, and one vaccinated person in the second generation. At least 3 of the 6 persons without symptoms had subclinical infection according to Downie's serological criterion. No preventive measures were taken. The disease was milder among the vaccinated.