Technical requirements for the licensing of pseudorabies (Aujeszky's disease) vaccines in the European Union.

Under the light of current scientific knowledge, particularly with the progress of molecular biology and of the definition of assays to be performed, it is possible to know, as accurately as possible, the biological properties of a vaccine. Most requirements of EP monographs and Directive 92/18 are founded on that concept. It is clear that there is a balance between safety and efficacy in the case of a live attenuated viral strain that means the more efficient a strain, the less safe it can be. Nevertheless, the problem is more complex; considerable progress has been done to set up new finished products and particularly with the adjuvants which are used now even in combination with live attenuated AD strains. The efficacy of a vaccine can be greatly enhanced, maintaining good local and general safety. But a debate always occurs when it is necessary to determine the acceptability threshold of a vaccine with regard to its safety and efficacy. The points of view are often very divergent. But, in any case, this threshold depends on the local conditions in the different countries. It is clear that objectives of a vaccination program and the requirements about a vaccine cannot be the same in heavily infected countries with a compulsory vaccination program as in countries or regions with a low prevalence of AD infection or with an absence of any infection. Moreover, it must also be considered that vaccines constitute only one element of a control or eradication program targeted against Aujeszky's disease virus.