An alternative In vitro method for evaluation of inactivated infectious bronchitis (IB) vaccines.

We report a rapid in vitro method for the potency evaluation of oil-based inactivated Infectious Bronchitis virus (IBV) vaccines. The method is designed to be used by both, quality control laboratories during vaccine manufacturing and by authorizing national laboratories. The simple technique reduces the time and the number of live birds needed for vaccine potency evaluation, effectively promoting a clean environment. Further, the method is a convenient alternative to using the traditional vaccine potency test in which live animals are used. To illustrate a proof of concept, antigens from a total of ten commercial oil adjuvant infectious bronchitis vaccines from different manufacturers were chemically extracted using isopropyl myristate and an antigen capture ELISA test was used to quantify the antigen concentration in the aqueous extracts. The results from the conventional live birds' tests, which determine the antibody titers after 3-4 weeks postvaccination, were compared to their corresponding antigen concentrations obtained by capture ELISA. The results indicate that, vaccines that contain a threshold amount of the specific IBV antigen (here determined to be > 1.26 pg/dose based on an antigen capture ELISA method), can be considered potent without the need to further test in live animals, provided that the concentration of the antigen can be reliably measured in its aqueous phase extract. Moreover, a linear relation between the antigen amount per dose and the antibody titer was found. Overall, the developed methods in this study are suited for high throughput vaccine potency evaluation.