Chimeric yellow fever 17D-Zika virus (ChimeriVax-Zika) as a live-attenuated Zika virus vaccine

Zika virus (ZIKV) is an emerging mosquito-borne pathogen representing a global health concern. It has been linked to fetal microcephaly and other birth defects and neurological disorders in adults. Sanofi Pasteur has engaged in the development of an inactivated ZIKV vaccine, as well as a live chimeric vaccine candidate ChimeriVax-Zika (CYZ) that could become a preferred vaccine depending on future ZIKV epidemiology. This report focuses on the CYZ candidate that was constructed by replacing the pre-membrane and envelope (prM-E) genes in the genome of live attenuated yellow fever 17D vaccine virus (YF 17D) with those from ZIKV yielding a viable CYZ chimeric virus. The replication rate of CYZ in the Vero cell substrate was increased by using a hybrid YF 17D-ZIKV signal sequence for the prM protein. CYZ was highly attenuated both in mice and in human in vitro models (human neuroblastoma and neuronal progenitor cells), without the need for additional attenuating modifications. It exhibited significantly reduced viral loads in organs compared to a wild-type ZIKV and a complete lack of neuroinvasion following inoculation of immunodeficient A129 mice. A single dose of CYZ elicited high titers of ZIKV-specific neutralizing antibodies in both immunocompetent and A129 mice and protected animals from ZIKV challenge. The data indicate that CYZ is a promising vaccine candidate against ZIKV.