Pre-and Post vaccine Measles Antibody Levels in Infants: An Evaluation of Routine Immunization in Nigeria

BACKGROUND: Measles is the vaccine preventable disease with the highest death toll. Despite the availability of potent measles vaccines for the past ten decades, measles still continues to occur both among vaccinated and unvaccinated infants especially in developing countries OBJECTIVE: This study was designed to assess the sero-conversion rate of among infants receiving measles immunization in Ilorin, Nigeria and also to determine the potency of measles vaccines administered. METHOD: The pre- and post measles vaccination sera of 400 children were tested using the Haemagglutination Inhibition test. The measles vaccines administered at the immunization centre were also tested for their potency using in-vitro titration method. RESULT: Only 286 (71.5%) of the vacinees returned to give post-vaccination samples. All the infants screened had low pre -vaccination measles antibody titres. Thirty one (8.0%) of the infants had measles prior to vaccination. The sero-conversion pattern showed that 196 (68.6%) of the infants developed protective antibody titres. Only 3(50%) of the 6 vaccine vials tested had virus titres of 10(-3.25) to 10(-6.3), which fell above the cut-off point recommended by the World Health Organization for measles vaccines. CONCLUSION: The sero-conversion rate of 68.6% observed among vacinees is far lower than the immunity level of 95% required to halt measles transmission in an endemic community. Failure of 31.4% of these infants to sero-convert post vaccination can be attributed partly to administration of sub-potent vaccines RECOMENDATION: There is need for improvement and maintenance of vaccine cold chain system in Nigeria, there is need for quality control to ensure the potency of vaccines administered at various vaccination centers.