Zika vaccines give 100% protection to mice, research finds

Scientists in the US believe they are a step closer to developing a vaccine to protect people from Zika. Research on mice has shown that two vaccines provided complete protection against the virus, prompting human trials to start by the end of the year.

Experts at the Beth Israel Deaconess Medical Centre, which is part of Harvard Medical School, the Walter Reed Army Institute of Research (WRAIR) and the University of Sao Paulo, found that mice given either jab did not pick up the Zika virus when they were exposed to it four or eight weeks later. One of them is a DNA vaccine developed at Harvard based on a Zika virus strain isolated in Brazil. The other is a purified, inactivated virus vaccine developed at WRAIR based on a Zika virus strain isolated in Puerto Rico.

The study, published in the journal Nature, showed that single shots of either vaccine protected mice against Zika. WRAIR is now developing its vaccine because it builds on "a type of vaccine that has been licensed before", according to Col Stephen Thomas, an infectious disease army doctor and head of the Zika vaccine programme at WRAIR. He added: "This critical first step has informed our ongoing work in non-human primates and gives us early confidence that development of a protective Zika virus vaccine for humans is feasible."

Dan Barouch, professor of medicine at Harvard Medical School, said "our data demonstrate that a single dose of a DNA vaccine or a purified inactivated virus vaccine provides complete protection" against Zika in mice.

Experts at WRAIR hope to start human trials by the end of the year. The research was supported by the National Institute of Allergy and Infectious Diseases (NIAID), part of the US National Institutes of Health. Jonathan Ball, professor of molecular virology at the University of Nottingham, said: "On the face of it, this is very good news and a significant step towards developing an effective vaccine to prevent Zika virus infection and the horrendous complications that this virus can sometimes cause. But we have to take these data in context, these were mice experiments and there is a long way to go before you can be sure that this vaccine candidate will perform in humans."

Professor Adrian Hill, director of the Jenner Institute at the University of Oxford, said the route to a human vaccine could prove difficult. "The DNA vaccine type tested is known to be a poor means of inducing antibodies in humans, and difficult to scale up to very large quantities, so better vaccine technologies are likely to be needed," he said.

“The other approach, a traditional one of inactivating the whole virus and adding an adjuvant, was more immunogenic and protective. But this would require use of the pathogen itself to manufacture it.”

The World Health Organisation (WHO) has declared Zika a global public health emergency and has warned it could spread to European holiday destinations this summer.

Zika is spread by mosquitoes and causes microcephaly and other severe brain defects in unborn children. It is also linked to the neurological condition Guillain-Barre syndrome. – PA