Issues of biological assays for viral vaccines.

The major test materials in viral vaccine production are seed virus, cell substrate and vaccine. The seed virus should be clearly identified as to source strain and its freedom from adventitious agents. The cell substrate to be used for the production of vaccine is generally tested following the recommendation that appeared in "Points to Consider in the Characterization of Cell Line Used to Produce Biologicals". It should be noted that a shift in emphasis has taken place from the earlier versions of the "Points to Consider". The tests for vaccine include bulk and final container tests. These tests, in principle, are performed following 21 CFR 600-680. In vitro and in vivo tests for detecting adventitious viruses are complementary; hence, both types of tests are desirable. Some of the practical points to consider in designing and performing the tests for adventitious viruses are discussed.