Level of mRNA expression of IFN-γ by fold change in experimental sheep inoculated with various forms of RVF vaccines from 1st day till the 12th months of 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.