Challenge with rubella virus after loss of detectable vaccine-induced antibody.

Studies were conducted of experimental challenge with rubella virus in vaccinees whose possession of vaccine-induced antibody after vaccination had been documented and whose antibody level had become undetectable or very low over time. The challenge virus was the Howell strain, which had been shown to produce typical clinical and laboratory features of rubella in susceptible persons. The challenge of the vaccinees resulted in local viral replication in all but one; in viremia, a primary immunologic response, and a secondary antibody response in some; and usually in illness without a rash or in subclinical infection. The results emphasize the importance of continuing careful clinical and laboratory surveillance of vaccinees for determining the persistence of vaccine-induced immunity and of considering methods for identifying and revaccinating the minority of vaccinees who lose such immunity.