Zika Vaccine Candidates Immunogenic and Safe in Phase 1 Trials

Two reports describe candidate Zika vaccines developed with traditional and innovative technologies.

Previously, a purified formalin-inactivated Zika vaccine (ZPIV) candidate derived from 2015 Puerto Rico virus was shown to protect mice and nonhuman primates against viremia after virus challenge. Investigators now report on phase 1, placebo-controlled, double-blind trials of ZPIV. Healthy adults at three US sites received either the vaccine or saline intramuscularly on days 1 and 29. Among 52 evaluable ZPIV recipients 92% seroconverted by day 57, as indicated by microneutralization titers of at least 1:10. Purified antibody from vaccinated participants infused into mice gave partial or complete protection from viremia after virus challenge. More than half had injection site pain or tenderness; systemic adverse effects (fatigue, headache, and malaise) were common, and one recipient reported a postvaccination severe systemic event.

The other report describes two DNA-based vaccine candidates, one with envelope protein containing Zika virus (ZV) and Japanese encephalitis virus (JEV) sequences and another with wild-type Zika sequences. Both had induced robust antibody responses in nonhuman primates. At three study sites the two vaccines were administered to healthy human adults using various schedules and two or three doses. Some 4 mg doses were split (2 mg in each deltoid) and some were given by needle-free injection. T-cell response was assessed using intracellular cytokine staining. Four weeks postvaccination positive antibody responses were seen in 60% to 89% of recipients of the first vaccine (JEV-ZV) and 77% to 100% of second vaccine recipients. All 14 recipients of the second vaccine by needle-free injection had positive antibody responses. Local and systemic symptoms were mild to moderate; no severe events were attributed to vaccination.