Zahra Bamouh, Zineb Boumart, Meryem Alhyane, Khalid Omari Tadlaoui, George E Bettinger, Douglas M Watts*, Ouafaa Fassi Fihri, Mehdi EL Harrak
Rift Valley Fever Virus (RVFV) is a mosquito-transmitted Bunyavirus capable of causing high morbidity and mortality among humans and domestic ruminants. Vaccination of domestic ruminants with vaccines that provide safe, rapid and long-term protection after a single vaccination is an effective strategy for protecting animals against Rift Valley Fever (RVF) disease. The aim of this study was to determine the duration and titer of antibody elicited by the RVF MP-12 del-NSm21/384 vaccine in sheep. Serum samples were collected from the animals before and after vaccination at various intervals up to one-year post vaccination to determine the duration of the antibody response using a virus-neutralizing test. All vaccinated sheep remained healthy, and RVFV antibody was first detected at two weeks post-vaccination in 37.5% of vaccinated sheep and 100% at three weeks pv. Neutralizing titers reached an average of 2.6 (equivalent dilution 1/400) at 2 months post vaccination and were maintained above 1.5 (equivalent dilution 1/35) for one year, thus providing evidence that a single vaccination elicited long lasting antibody in the animals. These antibody titers were at a level shown to be protective for sheep in a challenge study performed with virulent RVF ZH-501, further supporting the use of this vaccine virus strain as a candidate for long term protection of animals against virulent RVFV infection.