Determination of measles hemagglutination inhibiting antibody levels among school children in Ibadan, Nigeria.

Immune status of school children aged from 10-23 years against measles virus was determined by the hemagglutination-inhibition (HI) test with a view of assessing herd immunity. Blood samples from 500 schoolchildren were collected by finger-pricking in Ropacco filter papers. Sera were extracted in 1 mL of cold phosphate buffered saline and treated with 25% (w/v) kaolin and 50.0% monkey red blood cell (RBC) to a final concentration of 1:10. The measles hemagglutinating antigen used for the test was prepared from measles vaccine. Results showed that 62 (12.4%) were positive for measles HI antibody at a titer of 1:640, and 78 (15.6%) had a titer <1:10. There was no significant relationship (P > 0.05) between antibody titer and the schools, while a significant relationship (P < 0.05) existed between antibody titer and age. Although the majority of the schoolchildren had the measles antibody in their sera, titers were, however, beneath the threshold of protection in 33.4% of them. The significant association between age of the schoolchildren and HI titers showed that those antibodies were waning according to age. The study has shown a considerable high level of protection against measles among schoolchildren. To prevent future outbreak of measles among these schoolchildren, it will be advocated that a second dose of measles vaccine be administered.