Measles immunization. Successes and failures.

As a result of a large outbreak of measles, measles hemagglutination inhibition (HI) titers were measured in 465 immunized children. Titers of less than 1:4 were found in 14.6% of children immunized at 12 months of age as compared to 5.2% of those immunized at 13 months of age or later. Measles antibody titers were higher in the mothers of seronegative children who had been immunized at 11 or 12 months of age than in the mothers of seroposotive children. Measles HI titers of 1:4 or more were present in 94% of children immunized at 13 months of age or later between 1962 and 1964. The findings suggest that vaccine failure and not waning antibody accounts for the majority of titers of less than 1:4 in immunized children. Reimmunization programs should be considered for those who were immunized before 13 months of age.