Smallpox vaccination revisited. Some observations on the biology of vaccinia.

Sixty-two volunteers were studied to determine their local cutaneous, serologic, and virologic reactions to smallpox revaccination. Of 55 subjects available for examination, 45 (82%) had major cutaneous reactions. Subjects over 30 years old were more likely to have a major reaction. An increase in complement-fixing antibody titer was found in 74% of revaccinees with a major reaction. An increase in complement-fixing antibody titer was found in 74% of revaccinees with a major cutaneous reaction and is felt to be the best serologic indicator revaccination did not yield vaccinia virus. Cultures of the vaccination site demonstrated the virus to be present for a mean of 7.8 days (range 0--18 days) which coincided with separation correlate with antibody response. However, subjects vaccinated more than 3 years previously and subjects with major skin reactions shed vaccinia virus for longer periods than those vaccinated less than 3 years previously or who had equivocal reactions.