Antigenic Characterization of Poliovirus Strains by Neutralization Kinetic Studies and the Modified Wecker Technique

Poliovirus strains, both wild and Sabin-vaccine-derived, were studied by neutralization kinetic with antisera against the vaccine virus, and the results were compared with those obtained by the modified Wecker test. With type 1 and type 2 wild strains isolated in Japan, eleven type 1 strains and five type 2 strains were classified as heterologous to the vaccine strains in complete agreement by the two methods. One type 2 strain was classified as heterologous by the McBride test and intermediate by the modified Wecker test. As regards type 3 poliovirus strains, 17 wild strains were classified as heterologous by the McBride test, but the modified Wecker test discriminated only 9 as heterologous, while 4 other strains were classified as intermediate or homologous to the type 3 vaccine virus. Most of the poliovirus strains which were assumed as vaccine-related were classified as homologous or intermediate by the two methods, but some were classified as heterologous by the modified Wecker test and/or McBride tests. Detailed investigation of these strains by the reciprocal kinetic neutralization tests indicated that most of them were considered as nonvaccine-related. One of type 2 isolates and two of type 3 isolates from vaccinees in the field trial of 1961 could not be classified definitely. The data indicated that the McBride test is in some cases more suitable for the serological differentiation of poliovirus strains obtained in relation with Sabin vaccine feeding. It will be wise not to depend upon only one method in the serological differentiation of poliovirus strains, but better to use the two methods, as well as the reciprocal testing, if necessary.