Maternal vaccination protects dams and prevents in utero transmission of Rift Valley fever virus in rats

Rift Valley fever virus (RVFV) infection during pregnancy can cause abortion, fetal death, and vertical transmission, making pregnant individuals particularly susceptible to severe disease. This study evaluated the safety and efficacy of a live-attenuated RVFV vaccine lacking the NSs and NSm genes (RVFV-delNSs/NSm) in a pregnant rat model. Female rats were vaccinated either before or during pregnancy and later challenged with a virulent wild-type RVFV strain. Maternal survival, viral distribution, and fetal outcomes were then assessed. Vaccination, even at a high dose during early pregnancy, caused no adverse effects in either the dams or fetuses. Although low levels of viral RNA were occasionally detected in fetal tissues, no infectious virus was recovered. After challenge with wild-type RVFV, all vaccinated rats survived, whereas approximately 80% of unvaccinated animals died. No virus was detected in the organs of fetuses from vaccinated dams, indicating complete prevention of vertical transmission. Nearly all offspring from vaccinated mothers were born healthy without congenital abnormalities or low birth weight, while unvaccinated animals frequently experienced stillbirths and hemorrhagic lesions. Protection was also achieved when vaccination was performed before pregnancy. These findings suggest that deletion of NSs and NSm effectively attenuates RVFV while maintaining protective immunity, making this vaccine a promising candidate for preventing maternal infection and fetal transmission during pregnancy.
(AI)