A new Zika vaccine shows promising safety and immunogenicity, according to a phase 1 trial by the Vaccine Research Center at the NIH.

The speedy development of a Zika vaccine candidate was enabled by recent success in creating a vaccine for West Nile Virus—a closely related virus of the same genus—using the emerging DNA vaccine platform. Rather than introducing viral antigens or attenuated live virus, DNA vaccines consist of a plasmid containing genes for virus-specific proteins, allowing the host to produce antigen targets in situ.

The study, published online in The Lancet, evaluated the safety and immunogenicity of 2 DNA vaccine candidates (VRC5288 and VRC5283) in 125 healthy adult volunteers.

Subjects in the VRC5288 arm were randomized to 1 of 4 injection schedules, receiving a total of 2 or 3 intramuscular injections. Those in the VRC5283 arm received single (4 mg) or split doses (2 mg in each deltoid) given intramuscularly by syringe or needle-free device. All participants were followed for 24 months.

Both vaccine candidates were well tolerated, showing mild-to-moderate local and systemic symptoms common to vaccination. Blood cell analysis, however, indicated that the VRC5283 vaccine induced higher antibody titers and greater CD4 and CD8 T-cell responses.

The findings also highlight the significant impact that delivery method can have on patient response: The group that received a split-dose of VRC5283 showed a significantly greater magnitude of immune response compared with all other groups.

Based on these results, the VRC5283 formulation has been advanced into an international phase 2 efficacy trial. The trial aims to enroll at least 2,500 participants, and is expected to conclude in 2020.

Although the medical community is now closer to a possible Zika vaccine, which will prevent or reduce the severity of the infection's ocular manifestations in adults, it remains unknown whether or not inoculation will be protective against the viruses' teratogenic effects. Recent investigations have shown that congenital Zika syndrome causes severe brain and eye abnormalities, including microcephaly as well as macular and optic nerve defects.