ASSESSMENT OF FOOT-AND-MOUTH-DISEASE VACCINE POTENCY BY LIQUID-PHASE BLOCKING ELISA - A PROPOSAL FOR AN ALTERNATIVE TO THE CHALLENGE PROCEDURE IN ARGENTINA

The lowest expected protection (LEP) at a 95% confidence of 245 foot a nd mouth disease (FMD) commercial vaccines was calculated from the tit res of liquid-phase blocking sandwich ELISA (lpELISA) of cattle sera o btained from 3920 animals cat 60 days post-vaccination (d.p.v.) and ch allenged with live virus at 90 d.p.v. It was found that LEP evaluation is highly specific (i.e. it is able to predict the failure in 100% Of the cases) although its ability to predict the challenge (PG test) ap proval (i.e. sensitivity) comprised only 65% of the vaccines that pass ed the trial. It was possible, nevertheless to improve the sensitivity of the evaluation by using an alternative coefficient (Ro), exclusive ly dependent on the number of animals exhibiting the highest and lowes t lpELISA titres in a particular vaccine trial This coefficient was ca pable of predicting the PG approval of 90% of the vaccines yet maintai ning acceptable levels of safety (87% of specificity).Based on these r esults and as a first step towards the replacement of the challenge pr otocol in Argentina we propose a swift approval for commercialization of FMD vaccines which are able to reach the highly restricting LEP pas smark of 82%, and the rejection of those not reaching the 50% LEP limi t. More extensive experience with this new protocol will allow a finer adjustment of the LEP and Ro values and to set more precisely the cut -off points far direct approval or disapproval of vaccines by lpELISA, eliminating the use of live FMDV in the field.