A genetically stable Zika virus vaccine candidate protects mice against virus infection and vertical transmission.

Although live attenuated vaccines (LAVs) have been effective in the control of flavivirus infections, to date they have been excluded from Zika virus (ZIKV) vaccine trials due to safety concerns. We have previously reported two ZIKV mutants, each of which has a single substitution in either envelope (E) glycosylation or nonstructural (NS) 4B P36 and displays a modest reduction in mouse neurovirulence and neuroinvasiveness, respectively. Here, we generated a ZIKV mutant, ZE4B-36, which combines mutations in both E glycosylation and NS4B P36. The ZE4B-36 mutant is stable and attenuated in viral replication. Next-generation sequence analysis showed that the attenuating mutations in the E and NS4B proteins are retained during serial cell culture passages. The mutant exhibits a significant reduction in neuroinvasiveness and neurovirulence and low infectivity in mosquitoes. It induces robust ZIKV-specific memory B cell, antibody, and T cell-mediated immune responses in type I interferon receptor (IFNR) deficient mice. ZIKV-specific T cell immunity remains strong months post-vaccination in wild-type C57BL/6 (B6) mice. Vaccination with ZE4B-36 protects mice from ZIKV-induced diseases and vertical transmission. Our results suggest that combination mutations in E glycosylation and NS4B P36 contribute to a candidate LAV with significantly increased safety but retain strong immunogenicity for prevention and control of ZIKV infection.