Duration of the preservation of postvaccinal immunity against measles and the results of a repeat immunization of children with various initial antibody levels

The study of the blood sera of vaccinated children carried out by means of the indirect hemagglutination test with the use of dried erythrocytic diagnostic reagents prepared at the Pasteur Institute of Experimental Medicine, revealed that in groups free from measles infection for a long time immunity in children grew lower as the time elapsed since the date of vaccination increased. In 9-12 years antibody titers in the vaccines decreased, the percentage of children with protective titers dropping from 83.5 to 36.3. The revaccination of seronegative children ensured a significant increase in antibody titers in 51.6% of such children with the preservation of protective titers for 1 year (the term of observation). The repeated immunization of seropositive children with initial titers of 1:10 to 1:20 significantly stimulated their increase, lasting for a very short time, in 84.2-89.2% of children. In children with an initial antibody titer of 1:40 short-term seroconversion was detected only in 20-7% of cases, and in those with an initial titer of 1:80 no cases of seroconversion were observed. The data thus obtained suggest that the revaccination of seronegative children should be recommended.