ENZYME-LINKED-IMMUNOSORBENT-ASSAY IGG - ANTIBODY AVIDITY TEST FOR SINGLE-SAMPLE SEROLOGIC EVALUATION OF MEASLES-VACCINES

A measles-specific enzyme-linked immunosorbent assay (ELISA)-IgG avidi ty test for serologic evaluation of the efficacy of measles vaccines w ith only one blood sample was evaluated after vaccination with three m easles vaccine strains. Avidity indices were determined by the urea el ution technique in samples presenting antibody titers greater than or equal to 100 mlU/ml. All 127 sera collected 2-8 weeks after primary va ccination with Biken-CAM70 measles vaccine had low avidity indices (LA I, when less than or equal to 29%) with a time-dependent increase in a vidity. In samples collected 6-10 weeks after vaccination with Edmonst on-Zagreb, LAI were also observed in all 31 sera tested (mean = 15%) a nd in 233/242 (96.3%) filter paper samples from primary vaccination wi th Schwarz vaccine (mean = 14%). There was no difference in the mean a vidity among the three groups of primary vaccinees, although the Schwa rz group had higher antibody titers. In contrast, only 1/36 (2.8%) ser um samples from children who were seropositive at the time of measles vaccination had LAI (mean = 56%), despite the fact that they were coll ected early (2-5 weeks after vaccination). Of 90 serum samples from ch ildren vaccinated in the past with two doses and of 42 cord blood seru m samples, none had LAI. It is concluded that this test is a good tool for evaluating serologically the efficacy of a single dose schedule o f measles vaccine. With only one postvaccination sample, the test can discriminate nonresponders (antibody titers below 100 mlU/ml), primary responders (antibody titers greater than or equal to 100 mlU/ml with LAI), and those previously immunized (antibody titers greater than or equal to 100 mlU/ml with high avidity indices). The seroconversion rat e can be calculated after excluding the latter. (C) 1997 Wiley-Liss, I nc.