3 Zika vaccine approaches show early promise

Three different investigational Zika virus vaccine platforms have offered new hope against the deadly disease.

The three approaches - an inactivated virus vaccine, a DNA-based vaccine, and an adenovirus vector-based vaccine - protected against infection, induced immune responses and produced no adverse side effects when tested in rhesus macaques challenged with the Zika virus, according to a recent study.

Researchers first tested the inactivated Zika virus vaccine in 16 rhesus macaques, with eight receiving the experimental vaccine and eight receiving a placebo injection.

Within two weeks after the initial injection, all vaccinated animals developed neutralizing antibodies as well as antibodies specific to the viral envelope protein, a key vaccine target on the Zika virus.

A second dose was given four weeks later, which substantially boosted antibody levels. The monkeys were then challenged with Zika virus; following exposure, the vaccinated animals had no detectable virus and showed no other evidence of infection, while the group that received the placebo injection developed high levels of virus replication in the blood and other tissues for six to seven days.

In another experiment, the researchers administered two doses of an experimental DNA vaccine, one dose of an experimental adenovirus vector vaccine, or a placebo injection to three groups of four monkeys each.

The group that received the DNA vaccine received a booster shot four weeks after the initial vaccination. Minimal levels of antibodies were detected after the first injection. However, after the second injection, researchers detected Zika-specific neutralizing antibodies in the animals.

The adenovirus vector-based vaccine induced Zika-specific neutralizing antibodies two weeks after the single injection. Monkeys were exposed to Zika virus four weeks after the final vaccination, and both the DNA and adenovirus vector vaccine provided complete protection against infection.

These encouraging findings suggest a path forward for clinical development of Zika vaccines in humans, according to the researchers.

The study appears in the journal Science.