VIRUS CONTENT AND EFFECTIVENESS OF FOOT-AND-MOUTH-DISEASE VACCINES

The amount of 22 nm particles in 26 batches of cattle tongue epithelium extract used for the preparation of C-type vaccine was determined with an improved 50% hemolytic and point complement fixation test after fluorocarbon precipitation of non-immunizing 7 nm particles. The total amount of 22 nm and 7 nm particles (.alpha. GN [complement-fixing activity of untreated virus samples] value) varied considerably from batch to batch, 22 nm components (.alpha. GF [complement-fixing activity of fluorocarbon treated virus samples] value) showing a maximum 5-fold difference. Effectiveness of vaccines with known strain. In commercial C-type vaccines the complement-fixing activity of 22 nm particles and the potency of the vaccine showed a logarithmic regression (mouse index = -1.43 + 2.27 log .alpha. GF).