RA27/3 rubella vaccine. A four-year follow-up.

RA27/3 rubella vaccine was given to 418 subjects aged 1 to 17 years in 1974, 201 of whom participated in a four-year follow-up study. Two vaccine-associated complications were reported. A 5-year-old boy had transient arthritis of the hip, and a 1-year-old boy had a pigmented macule at the inoculation site. Rubella reinfection was uncommon, occurring at most in three of our subjects. All of the 186 susceptible children seroconverted, and 182 had hemagglutination-inhibiting (HI) titers of 8 or greater at four-year follow-up (geometric mean titer, 30.3). In the four children whose HI titers declined to undetectable levels, both HI and neutralizing (Nt) antibodies had developed immediately postimmunization, and two had Nt titers at follow-up despite loss of HI antibodies. RA27/3 vaccine boosted HI titers in 15 seropositive subjects, but titers returned to preimmunization levels four years later. We concluded that RA27/3 vaccine produced durable immunity with very low rates of rubella reinfection and secondary vaccine failure during the four years since immunization.