The potency testing of pseudorabies vaccines in pigs. A proposal for a quantitative criterion and a minimum requirement.

A criterion for the potency testing of pseudorabies vaccine based on the difference between the mean weight gain during the seven days after pathogenic challenge of vaccinated or control piglets is proposed. This criterion, termed delta G7, has been studied as a function of initial weight variation of the animals, different challenge strains and the period between challenge and the end of the test. The statistical analysis of results optimizes the experimental parameters and gives rise to a quantitative test which discriminates between vaccinates and controls and substantiates a proposal for a minimum vaccine potency requirement. The implementation of the method proposed is compatible with current practice in control laboratories.

The use of highly concentrated purified (by a large scale method) and long term liquid nitrogen stored foot-and-mouth disease viruses for the preparation of vaccines: physico-chemical quality controls and potency tests after storage.

In 1974 a new industrial technique for concentration and purification of FMD virus was presented at the OIE Conference. The bulk inactivated virus from this technique was stored in liquid nitrogen vapour until required for vaccine formulation. In 1981, having applied this technique regularly for seven years, we now describe the results obtained and the advantages gained in the field of trivalent O, A, C bovine vaccine production. Vaccines prepared from such bulk virus stocks after several years storage give good protection against virulent virus challenge.