INTERLABORATORY VALIDATION OF IN-VITRO SEROLOGICAL ASSAY SYSTEMS TO ASSESS THE POTENCY OF TETANUS TOROID IN VACCINES FOR VETERINARY USE

An interlaboratory validation study was carried out in seven laborator ies to evaluate the suitability of in vitro serological assay systems for the assessment of the potency of tetanus toroid in single and mult icomponent vaccines for veterinary use. Nine commercial vaccines and o ne experimental tetanus toroid preparation were selected for immunizat ion purposes according to Method A of the European Pharmacopoeia, Leve ls of tetanus antibodies in guinea-pig and rabbit serum samples were e stimated by indirect ELISA, toxin binding inhibition (ToBI) test, pass ive haemagglutination (HA) test and by the prescribed standard toxin n eutralization (TN) test in mice. Estimates of potency obtained by in v itro tests and by TN test were in good agreement for the various vacci nes tested and for antibody levels of individual serum samples in the range 2.6 IU/ml to 266 IU/ml. Significant(P < 0.05) intralaboratory va riation occurred less frequently for ELISA and ToBI test than for HA t est. The frequency of significant (P < 0.05) interlaboratory variation was acceptable for the ELISA and the ToBI lest but greater variation was observed for the HA test. It is concluded that the ELISA and ToBI tests are suitable in vitro assay systems for assessing the potency of tetanus toroid in batches of single and multicomponent vaccines for v eterinary use. Rigid standardization of the HA test is essential befor e this test can be used for the same quality control purpose.