Zika vaccine success in monkeys

Three new vaccines for Zika virus have been tested successfully in monkeys, and human trials are imminent, US researchers announced this week.

In February the World Health Organisation (WHO) declared the outbreak of Zika virus in Brazil a "public health emergency of international concern".

Scientists have since confirmed that Zika infection in pregnancy can damage the developing brain, particularly when infection occurs early in pregnancy, and last week UK researchers showed that up to 93 million people could contract the infection as the first wave of the epidemic sweeps across the Americas.

Now the US state of Florida has declared the first cases of the disease contracted inside America, and - for the first time - the CDC (Centers for Disease Control and Prevention) has advised against travel to some parts of the US for certain groups including pregnant women.

Some good news, then, is the successful testing in primates of a suite of anti-Zika vaccines being developed by a team based at Harvard Medical School, in Boston.

Writing in Science, Dan Barouch and his colleagues administered to a group of macaque monkeys either killed Zika virus that had been grown in culture, an experimental DNA vaccine construct comprising the DNA message encoding part of the Zika virus outer coat, or an adenovirus related to the "common cold" that had inserted into it part of the Zika virus coat.

In all three cases the recipient animals were completely protected against subsequently challenge with a large dose of Zika virus and without any ill effects. It was also possible to transfer antibodies against Zika made by the vaccinated monkeys to un-immunised animals and protect them too, proving that the vaccine prevents infection by stimulating the production of antibodies that neutralise the virus.

This is important, Barouch points out, because this establishes a benchmark for the antibody levels required to successfully defend an individual against the infection, and future vaccine performance can be measured against this as vaccine development proceeds.

"We're developing three vaccine technologies in parallel because, in human clinical trials, one agent might not perform well, so we need additional options," Barouch explains.

The success of the trial in monkeys, which are close relatives of humans, is a good predictor of the safety and effectiveness of the vaccines in humans.

"Clinical trials with the killed vaccine candidate are scheduled to commence in the fall," says Barouch.