Factors influencing the stability of acid-precipitated polyvalent Bordetella pertussis bulk suspensions.

According to the statistical analysis of the potency values of acid precipitated polyvalent bulk suspensions of Bordetella pertussis, the potency of suspensions decreased below 8 IU/30 IOU during storage for 5 to 9.8 years. The average annual decrease over a 13-year period was 2.03 IU/30 IOU. The periodicity in the decrease of potency values was assumed to be connected with changes in the quality of the casein hydrolysate ingredient of the medium. Periodic functions employed to approach potency values with limits of 1 SD falling within the range of 64--156% indicated that the potency decreased below 8 IU/30 IOU after 9 years.