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 avidity test for serologic evaluation of the efficacy of measles vaccines with only one blood sample was evaluated after vaccination with three measles vaccine strains. Avidity indices were determined by the urea elution technique in samples presenting antibody titers > or = 100 mIU/ml. All 127 sera collected 2-8 weeks after primary vaccination with Biken-CAM70 measles vaccine had low avidity indices (LAI, when < or = 29%) with a time-dependent increase in avidity. In samples collected 6-10 weeks after vaccination with Edmonston-Zagreb, LAI were also observed in all 31 sera tested (mean = 15%) and in 233/242 (96.3%) filter paper samples from primary vaccination with Schwarz vaccine (mean = 14%). There was no difference in the mean avidity among the three groups of primary vaccinees, although the Schwarz group had higher antibody titers. In contrast, only 1/36 (2.8%) serum samples from children who were seropositive at the time of measles vaccination had LAI (mean = 56%), despite the fact that they were collected early (2-5 weeks after vaccination). Of 90 serum samples from children vaccinated in the past with two doses and of 42 cord blood serum samples, none had LAI. It is concluded that this test is a good tool for evaluating serologically the efficacy of a single dose schedule of measles vaccine. With only one postvaccination sample, the test can discriminate nonresponders (antibody titers below 100 mIU/ml), primary responders (antibody titers > or = 100 mIu/ml with LAI), and those previously immunized (antibody titers > or = 100 mIU/ml with high avidity indices). The seroconversion rate can be calculated after excluding the latter.