An extremely attenuated, live measles virus vaccine (CAM-EX). Persistence of low titer-antibody in institutionalized children with psychomotor retardation after vaccination.

Fifty children with psychomotor retardation, who had no detectable measles hemagglutination-inhibition (HI) antibody, were vaccinated with an extremely attenuated, live measles virus vaccine (CAM-EX). Only 10% of the children had fever after vaccination. No other symptoms were observed. Forty of 44 vaccinated children showed increase in HI antibody titers of 2(3) or more, with a geometric mean titer of 2(4.2). A five-year follow-up study revealed that the initially low-titer antibodies persisted well under conditions without a booster response due to natural measles.