Accidental vaccinia may occur either in a recently vaccinated person through autoinoculation by vesicular fluid or in a person who is in close personal contact with a recently vaccinated person. Though oral lesions of accidental vaccinia are not uncommon, an outbreak of similar oral lesions in a family is unusual.
Greer KE, Sheap CN. A Family Outbreak of Oral Accidental Vaccinia. Arch Dermatol. 1974;110(1):107-108. doi:10.1001/archderm.1974.01630070071019