An international consensus as to the best method for measuring the potency of inactivated poliovirus vaccines (IPV) in vitro or in vivo has not yet been achieved. Laboratories do not agree on the most feasible animal model of potency and therefore laboratories use rats, guinea pigs, chickens or primates none of which are ideal for many reasons. In the U.S. and Canada, the monkey is required for the purpose of IPV lot release. Monkeys are given 3 injections at 7 day intervals. This hyper-immunization may obscure the antigenicity. The new purified vaccines induce an antibody response in monkeys that would rarely fail a vaccine lot even if the level of D Ag unit in the vaccine was lower than would be recommended for a human dose. For these reasons we are pursuing the identification of an appropriate animal model. We have selected the Balb/c mouse for further study. Based on the manufacturer's assigned potency, serial two-fold dilutions of trivalent IPV were prepared. The potency of the first vaccine dose was equivalent to a human dose. Six groups of mice were immunized intraperitoneally with one injection. Neutralizing antibodies were measured at 21 days. The potency of the six preparations of vaccine was measured by ELISA. The correlation between the amount of antigen injected and neutralizing antibody response was R=0.90, R=0.85, R=0.89 for poliotypes 1, 2 and 3 respectively. We are in the process of expanding this approach to confirm its usefulness.
