Attenuated rubella viruses. Laboratory and clinical characteristics.

AFTER THE isolation of rubella virus in 1962, 1,2 many investigators directed their attention toward studies that were to characterize the agent, define the nature of the disease, and eventually lead to vaccine development. The initial efforts of several groups to produce inactivated rubella virus vaccines were disappointing. Completely inactivated materials were usually not antigenic, and experimental preparations that did elicit an antibody response were thought either to contain residual live virus or to confer no protection to a rubella challenge. 3,4 Early attempts to develop a live rubella virus vaccine were also unrewarding. A number of separate research teams prepared experimental materials from virus strains arbitrarily passed varying numbers of times in cell cultures. 5-9 Unfortunately, these viruses were not attenuated, and recipients contracted rubella with rash and, in many instances, transmitted their infection to susceptible contacts. At this time, our laboratory was likewise engaged in passing strains of