TRIALS OF EDMONSTON-ZAGREB MEASLES-VACCINE IN GUINEA-BISSAU - SEROLOGICAL RESPONSES FOLLOWING VACCINATION WITH EDMONSTON-ZAGREB STRAIN AT 4-8 MONTHS VERSUS VACCINATION WITH SCHWARZ STRAIN AT 9-12 MONTHS OF AGE

In two trials of measles vaccination in Guinea-Bissau, children were r andomized to receive either the Edmonston-Zagreb (EZ) virus at age 4-8 months or, as a control group, a standard dose (5000 p.f.u.) of the S chwarz (STY) virus at 9-12 months. In the first trial a medium dose of EZ virus (40000 p.f.u.) was used and in the later trial a high dose ( 150000 p.f.u.). Pre- and postvaccination blood samples were analysed w ith a haemagglutination inhibition (HAI) test and an enzyme-linked imm unosorbent assay (ELISA). For the ELISA the blood samples were collect ed on filter paper. Of 362 prevaccination specimens, 18 and 55%, respe ctively, were positive in the ELISA and HAI tests. At 18-20 months, th e children who had received the EZ vaccine had a seropositivity of 91% by the ELISA method and one of 89% by the HAI method. The equivalent values for the SW group of children were 100 and 96% respectively. Ant ibody levels in the EZ group, as measured by either method, were signi ficantly, lower than the levels in the SW group. The serological resul ts of the present study suggest that lowering the age at measles vacci nation to below 9 months is feasible. However, further studies are nee ded to determine which virus strain, dosage and age at vaccination wil l prove to be optimal in countries where severe measles is common befo re the age of 9 months.