VRC 705: A Zika Virus DNA Vaccine in Healthy Adults and Adolescents

This was a multicenter, randomized study to evaluate safety, immunogenicity, and efficacy of a 3-dose vaccination regimen with the Zika virus wildtype (ZIKVwt) DNA vaccine (VRC-ZKADNA090-00-VP) or placebo (VRC-PBSPLA043-00-VP). The placebo was a sterile phosphate-buffered saline (PBS). The hypotheses were that the ZIKVwt DNA vaccine would be safe and would elicit a ZIKV-specific immune response. Participants received study product intramuscularly (IM) in the limbs as specified by the group assignment by PharmaJet needle-free device. In Part A, 90 participants were randomized to vaccine at a 1:1:1 ratio to receive a 4 mg dose split between 2 injections, 4 mg dose split between 4 injections or 8 mg dose split between 4 injections. In Part B, 2338 participants were randomized to vaccine or placebo in a 1:1 ratio to receive a 4 mg (1 mL) dose of vaccine or 1 mL of placebo split between 2 injections. The vaccine dose and administration plan for Part B was selected based on Part A and Phase 1 data. Vaccine safety and tolerability were assessed by monitoring of clinical and laboratory parameters throughout the study. Solicited reactogenicity symptoms were collected for 7 days after each product administration. The study schedule included clinic visits with safety and immunogenicity blood samples collected at particular time points. Vaccine efficacy was evaluated in Part B by comparing incidence of virologic ZIKV cases between vaccine and placebo groups. During the study, when participants exhibited any possible symptom of ZIKV infection, they were evaluated by blood and urine ZIKV polymerase chain reaction (PCR). Stored blood samples were also assessed retrospectively by ZIKV PCR to identify possible asymptomatic cases. A Data and Safety Monitoring Board (DSMB) oversaw the study.