The reduction of animal usage by the application of indirect haemagglutination in the potency testing of diphtheria toxoid in combined vaccines.

Eight Adsorbed Diphtheria-Tetanus vaccines and 13 Diphtheria-Tetanus-Pertussis vaccines made by four different manufacturers were tested for the potency of the diphtheria components in guinea-pigs by the method of British Pharmacopoeia (1973). Two-hundred-and-ten guinea-pig sera consisting of ten sera related to each vaccine sample thus obtained were titrated for diphtheria antitoxin by indirect haemagglutination (IHA) and the conventional toxin neutralization (TN) tests. Statistical analysis of the results showed a good correlation between the titres obtained with the two tests. The potencies of the diphtheria components of various vaccines calculated from the antitoxin content of the respective guinea-pig sera titrated by the IHA test correlated significantly with the potencies obtained from the antitoxin content titrated by the routinely used TN test. The use of IHA in place of the TN test thus offers as an alternative that permits a reduction in animal usage.