Measles Vaccine Expressing the Secreted Form of West Nile Virus Envelope Glycoprotein Induces Protective Immunity in Squirrel Monkeys, a New Model of West Nile Virus Infection

West Nile virus (WNV) is a mosquito-borne flavivirus that emerged in North America and caused numerous cases of human encephalitis, thus urging the development of a vaccine. We previously demonstrated the efficacy of a recombinant measles vaccine (MV) expressing the secreted form of the envelope glycoprotein from WNV to prevent WNV encephalitis in mice. In the present study, we investigated the capacity of this vaccine candidate to control WNV infection in a primate model. We first established experimental WNV infection of squirrel monkeys (Saimiri sciureus). A high titer of virus was detected in plasma on day 2 after infection, and viremia persisted for 5 days. A single immunization of recombinant MV-WNV vaccine elicited anti-WNV neutralizing antibodies that strongly reduced WNV viremia at challenge. This study demonstrates for the first time the capacity of a recombinant live attenuated measles vector to protect nonhuman primates from a heterologous infectious challenge.