A Controlled Trial of Medium Titre Measles Vaccination at Six Months of Age: Prospective Study

Abstract: In a rural community comprising 35000 population, 510 infants born within a ten-month period were enrolled from a birth cohort. They were allocated into three equal groups of 170 Two types of measles vaccin es, namely medium titre (4.7 log pfu/ml) Edmonston­ Zagreb(EZ) or an equivalent dose of Connaught(CON) vaccine were used in a double blind randomized trial to compare their immunological response in infants aged five months. The third group of infants acted as a control and was vaccinated with standard titre (3.9 log pfu/ml) Schwarz vaccine at nine months of age. Measles antibody titres were measured before and 18 weeks after vaccinati on using plaque neutraliution assay: All vaccine groups were monitored for the first three weeks for any adverse reaction and were then prospectively followed up for 60 months. The mean age of the infants was 20.2 weeks and the three groups were comparable as regards to nutrition. health, family and socioeconomic characteristics. No severe side effect of any of the vaccines used was reported and there were no significant differences in the rates of adverse reactions between the vaccine groups and the control group. Sera of 153(900/o)of the EZ recipients and 149(88%) of the CON group showed seroconversion rates of 71 % and 78%, and seropositivity rates of 71% and 69°/o, respectively. Follow up of the infants showed that early medium titre EZ vaccine conferred adequate clinical protectivity against measles infection for five years. Thirty months after vaccination, a total of 35 deaths were reported: 14 in the EZ group, of whom 10 were females; 13 in the control group including six females; and eight infants from the Co naught group. The mortality rate among females within the Edmonston­ Zagreb vaccinee was just significantly higher than that of males (p<0.05).