Improved ELISA test for determination of potency of Inactivated Poliovirus Vaccine (IPV)

An improved ELISA test for determination of potency of Inactivated Poliovirus Vaccine (IPV) is proposed. The method is based on the use of IgG purified from immune rabbit serum conjugated with biotin. Optimized and validated materials for the test can be stored for a long time in the form of ready-to-use kits. Optimization included selection of anti-poliovirus rabbit antibody batches with the best specificity to D-antigen as well as finding the most efficient parameters for all steps of ELISA protocol. The assay is based on direct (“sandwich”) ELISA scheme, in which antigens are captured on ELISA plates coated with purified rabbit polyclonal D-antigen specific IgG raised against wild polioviruses of three serotypes. D-antigen specificity of the IgG was at least 10 times higher than to H-antigen (heat-inactivated virus). The presence of antigen was detected using biotin-conjugated IgG from the same source. Eight-point dose-response curves were obtained for each sample and the reference vaccine. The protocol ensured low background (less than 0.2 OD), linear response over the entire range of optical density measurements (up to 3.0 OD), and high precision of data (assay variability was about 3%). The quantitative results and the validity of the test were determined by two numerical approaches, linear regression and a new analysis procedure called the local interpolation method. For the first approach we also proposed a new method for testing of parallelism of regression lines. The ELISA protocol for all three types of poliovirus is based on standard off-the-shelf reagents, and is highly reproducible and reliable. An in-house Reference Reagent was formulated and calibrated against the International Reference for IPV.