ABSTRACT
The Nigerian Expanded Programme on Immunization (EPI) was assessed with particular reference to measles immunization. Of 150 children who received measles vaccine at the Institute of Child Health, University of Ibadan, Nigeria, 82 (54.7%) seroconverted. The immune response was directly related to the titre of the vaccines used. Vaccines whose titres were 10(-1) to 10(1.7) stimulated immune responses in 0-25% of vaccinees, those with titres in the range 10(-2.1) to 10(-2.5) stimulated responses in 12-47.6%, while those with titres of 10(-2.7) to 10(-3.4) stimulated responses in 87.5-100% of vaccinees. Only one of the vaccines used had a titre that met the minimum WHO required standard of log 10(-3) TCID50 at the point of vaccination
Subject(s)
Antibodies, Viral/isolation & purification , Child, Preschool , Drug Stability , Hemagglutination Inhibition Tests , Infant , Measles Vaccine/immunology , Measles Vaccine/microbiology , Measles Vaccine/standards , NigeriaABSTRACT
The efficacy of standard potency Edmonston-Zagreb (E-Z) measles vaccine was tested in a randomized trial of Black infants in a rural area of South Africa where a measles epidemic was occurring. The following immunization schedules were used: 48 infants aged 4-8.5 months who received 3.9 log 50 infectious units of E-Z vaccine (group A); 48 infants aged 4-8.5 months who received 3.28 log 50 infectious units of Schwarz vaccine (group B); and 28 infants aged greater than 9 months who received 3.28 log 50 infectious units of Schwarz vaccine and served as controls (group C). For infants aged less than 23 weeks who were given either the E-Z or Schwarz vaccine, the number of seropositives was low (28%), irrespective of the pre-vaccination level of measles antibody. There was a higher number of seropositives (68%) among those in the age range greater than 23 weeks to less than 36 weeks who received the E-Z vaccine rather than the Schwarz vaccine (36%). When administered to children aged greater than 36 weeks, the Schwarz vaccine produced a satisfactory, though suboptimal response rate (61%). There was no correlation between seropositivity and pre-vaccination measles antibody status. Use of the standard dose of E-Z vaccine may have been one of the factors for this poor response, and this supports the WHO recommendation that titres higher than the standard potency vaccine are needed if 6-month-old infants are to be successfully immunized against measles