Optimal age for vaccinating Nigerian children against measles. II. Seroconversion to measles vaccine in different age groups.

Ninety-eight children between five and nine months were given measles vaccine. Bloodsamples were taken before and again six to eight weeks after immunization and tested for haemagglutination inhibition antibodies to measles virus. It was found that the sero-conversion rate was significantly lower (p less than 0.05) in infants under seven months than over this age. The results suggest that although some immunized at six months of age show seroconversion, the proportion is too small to justify extensive immunization at this age. It is proposed that children in Lagos should be immunized from the age of eight to nine months.