Congenital vaccinia: Infection of the fetus in the last trimester of pregnancy due to bloodborne dissemination of the vaccinia virus in the pregnant woman after she has received a smallpox vaccination. The affected infant is often premature. The skin lesions in the newborn infant are like a fresh vaccination but often confluent and extensive. Death almost always occurs before birth or shortly thereafter. To prevent this dire disorder, it is recommended that pregnant women not be vaccinated unless special circumstances may call for it (e.g., they have been exposed to a smallpox patient or are a household member of a smallpox case).