Viremia, virus excretion, and antibody responses after challenge in volunteers with low levels of antibody to rubella virus.

After intranasal challenge of volunteers with rubella virus vaccine, viremia was assayed by inoculation of lymphocytes and whole blood from vaccines into Vero cell cultures. Viremia was detected in one of 19 volunteers with low levels (less than or equal to 15 IU) of preexisting vaccine-induced antibody to rubella virus, in eight of 10 seronegative volunteers, in none of 10 seropositive volunteers (antibody level, greater than 15 IU), and in none of 12 volunteers with low levels of preexisting naturally acquired antibody. Excretion of the virus was detected in four volunteers with preexisting vaccine-induced antibody but in none with naturally acquired antibody; eight of 10 seronegative volunteers excreted virus. After challenge, all volunteers with low levels of preexisting vaccine-induced antibody developed booster antibody responses that were measured by radioimmunoassay, and low levels of rubella-specific IgM were detected in four volunteers by M-antibody capture radioimmunoassay. One seronegative, one seropositive, and five low-titer volunteers developed arthralgia. The risk of viremia after challenge in individuals with low levels of rubella antibody appears to be low but may be higher than usual when immunity is induced by rubella vaccine.