Clinical and serologic study of four smallpox vaccines comparing variations of dose and route of administration. Standard percutaneous revaccination of children who receive primary subcutaneous vaccination.

Six months after subcutaneous vaccination with one of four smallpox vaccines, 655 children were challenged with a standard percutaneous smallpox vaccine. Response to reimmunization was characterized by a significant acceleration and diminution of skin response, but not to the degree seen in an equivalent group who had received their primary immunization percutaneously. Fever after revaccination was absent if there had been a "take" with primary subcutaneous vaccination. The overall incidence of minor vaccine-related complications with revaccination was 2-1/2%. The neutralizing antibody response to revaccination was markedly reduced, as compared to that of children who received either one or two successful percutaneous vaccinations. Subcutaneous vaccination followed by percutaneous vaccination is not recommended as a schedule for smallpox immunization, because complications are not avoided, and the incidence and mean titer of resultant neutralizing antibody are low.