Poultry vaccines: an analysis of the animal trials required for vaccine testing and the way to reduce or refine these tests.

The testing of vaccines for use in chickens requires a large number of animal trials. Especially for poultry vaccines, quality testing of each batch consists of testing for extraneous agents in chickens for all products and potency tests for inactivated products. For the licensing of a vaccine a number of safety and efficacy tests is necessary. The safety testing covers dose and overdose studies, and the influence on reproductive performances and immunological functions. For live vaccines some additional trials concerning spread of vaccine strains, dissemination in the vaccinated animals and reversion to virulence are required. Some possibilities for combining several tests are presented. The purpose is to reduce the number of animals needed in these trials. The efficacy testing mostly requires challenge tests to define onset, level and duration of immunity. Serological test systems to replace the challenges are rarely implemented. The example of efficacy testing of infectious bursal disease vaccines demonstrates the possible replacement of a challenge by a serological test system. Parameters are morbidity, mortality, histological findings, bursa/body-ratios, and humoral antibodies detected by serum neutralization and ELISA.