[Experimental study of postvaccinal immunity to sheep-pox]

Two live virus sheep-pox vaccines have been prepared on lamb testicular cells from strains Perego and RM65. Inocuity and activity have been compared to those of a commercial vaccine on a small number of lambs. Immunogenicity has been studied through neutralizing and precipitating antibodies, and through challenge resistance (strain Held), using a protective index. Results show that Perego vaccine titrated at 10(4) DICT50 gives a reliable immunity and does not provoke severe reaction post-inoculation. RM65 vaccine of which protection index is lower, only avoid infection to generalize. Although some correlation exists between seroneutralizing titers and protective index, virulent challenge appears and seems to give better data with regards to the level of protection conferred.