The role of hypersensitivity in the pathogenesis of vaccinia virus infection in humans

To evaluate the role of delayed hypersensitivity in the pathogenesis of the primarysmallpox vaccination reaction, 26 previously unvaccinated children were repeatedly inoculated with vaccinia virus at 2 day intervals. Infectious and noninfectious virus were applied simultaneously at different sites each time. The incubation periods of the papules and the vesicles for the second vaccination were significantly shorter than those of the first. Hypersensitivity to vaccinia virus was apparent within the developmental period of the first vaccination. The shortened incubation period of the second vaccination indicated that delayed hypersensitivity participated in the pathogenesis of the primary lesion.