The 40Fp8 vaccine strain is safe and protects pregnant ewes from a virulent RVFV challenge

In the present study, we evaluated the immunogenicity, safety and protective efficacy of the attenuated RVFV-40Fp8 strain in natural hosts (non-pregnant ewes) and in a highly susceptible host infection model such as pregnant ewes in the first third of pregnancy. Our results confirm the immunogenicity of 40Fp8 administration in non-pregnant and pregnant ewes, as well as the absence of foetal damage even after a high-dose vaccination regime in pregnant ewes. In addition, the ewes and their foetuses were protected against a virulent RVFV-56/74 strain challenge, as shown by comparative evaluation of blood, serum and different tissue samples from vaccinated and non-vaccinated pregnant ewes. These results confirm the potential use of 40Fp8 as a RVF live-attenuated vaccine candidate and pave the way for further clinical developments.