An Examination of the Safety and Efficacy of Aripo-Zika as a Zika Virus Vaccine Candidate

Flaviviruses are a genus of vector-transmitted viruses that are nearly globally distributed, and flavivirus infections can result in life threatening diseases. Many flaviviruses such as Dengue, West Nile, yellow fever and Zika viruses are globally distributed. Zika virus (ZIKV) is a single strand positive-sense RNA virus, and its disease has been linked to Guillain Barré Syndrome (i.e., a debilitating autoimmune disorder that affects the nerves) in adults and congenital birth defects including microcephaly (i.e., a neurodevelopmental disorder due to impaired neural cell proliferation) in newborns. Insect-specific flaviviruses (ISFVs) are understudied given their apathogenic characteristics to humans and animals. However, given their close genetic relationship to vertebrate infectious flaviviruses, ISFVs can serve as a delivery system (i.e., vector) for flavivirus antigenic proteins. Aripo virus (ARPV) is a recently discovered ISFV isolated in Trinidad. We developed a chimeric Zika vaccine, Aripo-Zika, by substituting the pre-membrane and envelope genes of ZIKV into the ARPV genome. Here, we explored (i) the efficacy of Aripo-Zika (AZ) vaccination by evaluating passive transfer of maternal antibodies, (ii) the optimal dosage regimen, (iii) anti-vector immunity to the ARPV backbone, and (iv) the effects of boosters on vaccine efficacy. We also evaluated AZ safety via a co-infection study. Our results show a near linear relationship between increased dose and immunogenicity, with 1011 genome copies being the most effective minimum dose administered. Inclusion of boosters further increased the immunogenicity of AZ. Additionally, prior immunization with AZ showed minimal effects on subsequent immunization with an ARPV-West Nile virus (AWN) vaccine candidate, confirming the applicability of the ARPV backbone to multiple flavivirus vaccine candidates. In vitro co-infection of ZIKV with ARPV, and ZIKV with AZ in African green monkey kidney cells (i.e., Vero-76) indicated ARPV and AZ remain incapable of replication in vertebrate cells, even in the presence of active ZIKV replication. Altogether, our data suggests that the ARPV platform is a safe and effective strategy for the development of flavivirus vaccines.