A new freeze-dried living virus vaccine against sheep-pox.

A sheep-pox virus strain has been adapted and multiplied in primary lamb kidney cell cultures. The main characteristics of the strain have been verified in vitro after clones were isolated, and the results confirmed its identity. The safety and the potency of the strain have been investigated in sheep. The inoculation of the strain to sheep was followed by a post-vaccinal reaction materialised by a nodule at the site of inoculation and an increase of temperature by about 1 degree C. No reactions adversely affecting pregnancy have been noted. Immunisation was demonstrated by an increase in the level of neutralising serous antibodies and protection against the pathogenic virus. The immunity tended to decrease during the second year after primovaccination and a yearly booster vaccination appeared to be necessary. Primovaccination of lambs over 2 months of age produced a better immunity, especially when the lambs were born from vaccinated ewes. This strain forms the active principle of a freeze-dried vaccine containing no adjuvant of the immunity.