Recovery of protective activity in rabies virus vaccines concentrated and purified by four different methods.

Rabies vaccines concentrated by ultrafiltration, zinc acetate precipitation, ammonium sulfate precipitation, or aluminum phosphate gel adsorption were compared with respect to recovery of protective activity and purity, as measured by protective activity per mg of protein. Vaccine obtained by ammonium sulfate precipitation had a better recovery rate and a higher purity than those prepared by the other methods. Potent vaccines were also obtained by the zinc acetate precipitation and aluminum phosphate gel adsorption methods, whereas ultrafiltration was the least satisfactory method from the standpoint of vaccine purity. Chromatography of virus concentrated by ultrafiltration on a cellulose ion exchange column reduced the level of nonviral proteins. The protective activity data obtained for the vaccines examined in these experiments were found to correlate with the vaccine's complement fixation titer per mg of protein.