Protection of MP-12-Vaccinated Rhesus Macaques Against Parenteral and Aerosol Challenge With Virulent Rift Valley Fever Virus

To test safety and efficacy of the Rift Valley fever MP-12 (RVF MP-12) vaccine, 9 healthy adult Rhesus macaques, weighing 5-10 kg, were inoculated intramuscularly with 6 x 10(3) plaque forming units (PFUs) of MP-12 vaccine. The monkeys developed neutralizing antibody responses with no adverse effects other than a transient, low-titer viremia in 3 monkeys. Four vaccinated animals challenged intravenously with 3 x 10(6) PFUs of virulent Rift Valley fever virus strain ZH-501 (RVFV ZH-501) at 126 days after vaccination were protected against infection. The remaining 5 vaccinated monkeys along with 2 monkeys that had been vaccinated 6 years prior were completely protected against a small particle aerosol challenge of 5 x 10(5) PFUs of RVFV ZH-501. The mutagen-attenuated RVF MP-12 vaccine was determined to be protective against intravenous and aerosol challenge with virulent RVFV in these macaques, which suggests further development as a vaccine for humans is warranted.