The mean neutralizing index in experimental sheep inoculated with various forms of RVF vaccines from pre (day before inoculation) till the 13th months after inoculation the data expressed as mean ± SEM, p<0.05. G1: Control negative, G2: Sheep inoculated with AlHV, G3: Sheep inoculated with Ch-NPsV, G4: Sheep inoculated with AlP-NPsV.