Evaluation of the use of various rat strains for immunogenic potency tests of Sabin-derived inactivated polio vaccines

Effects of the thermal denaturation of Sabin-derived inactivated polio vaccines on the D-antigenicity and the immunogenicity in rats

The efficacy of a Sabin-derived inactivated polio vaccine (sIPV) can be evaluated by measuring the immunogenicity and the contents of D-antigens, which induce the neutralizing antibodies. The immunogenic potency test in rats was done as a national assay in Japan. The two manufacturers of sIPV in Japan have performed both assays since development, and there is no clear discrepancy between the results obtained in the two assays. To further know the relationship between the two assays, we analyzed the effects of the heat treatment of sIPV on the D-antigenicity and the immunogenicity. We observed that the marginal D-antigen that remained after the thermal treatment was capable of inducing relatively high neutralizing antibodies in rats. This indicates that the measurement of the D-antigen contents as part of the quality control of sIPV is more sensitive and appropriate to detect denatured vaccines.

[Polio vaccines and biorisk management of polioviruses]

Japan is the first country where inactivated polio vaccines derived from Sabin attenuated strains, which are used to manufacture oral polio vaccines, were introduced in routine immunization program. The Sabin-derived inactivated vaccine has been developed based on the fact that Sabin strains are less neurovirulent and manufactured at safer productionfacilities than wild polioviruses. It is also convincing that Sabin strains are more safely used for evaluating the efficacy of inactivated vaccines in rat immunogenicity tests. However, in the current situation where polioviruses are close to being eradicated, the facilities that manufacture vaccines and/or conduct quality control of them are needed to meet the biorisk management requirements established by WHO, which are based on the Polio Eradication & Endgame Strategic Plan 2013-2018. At present, type 2 polioviruses including Sabin 2 strain should be contained in the facilities which meet the WHO biorisk management requirements. The respective facilities are expected to give full consideration based on a careful risk assessment of viral transmission not only to personnel, but also to the environment and the community around the facilities, and the establishment of biorisk management will be needed. Thus, the facilities handling and storing infectious polioviruses must be certified as poliovirus-essential facilities following the WHO biorisk management requirements.