Zika Virus: Scientists claim to have identified a vaccine that could stop the epidemic

Scientists believe they are on the cusp of developing a vaccine to protect people from the Zika virus.

Two new studies released today have identified antibodies that halt the infection by binding strongly to it.

The first, by the Washington University School of Medicine, studied antibodies from the Zika virus itself which successfully neutralized African, Asian and American strains of the infection.

Meanwhile University of North Carolina scientists examined antibodies produced by survivors of dengue fever, a similar mosquito-borne virus.

Both discoveries have been hailed as some the most precise investigations into Zika to date as the virus sweeps the world - and threatens to infect millions more before the epidemic burns out.

They have emerged just a day after the US Health Department started the first human trials of another experimental vaccine.

The first study by the Washington University School of Medicine was published in the journal Cell.

It identified six antibodies that bound strongly to Zika virus, and the precise spot on the virus that the antibodies recognized.

Study co-senior author Professor Daved Fremont said: 'Importantly, some of our antibodies are able to neutralize African, Asian and American strains of Zika virus to about the same degree.

'A vaccine designed to elicit similar antibodies might be able to protect people from Zika strains worldwide.'

Testing mice, Professor Fremont's team used a technique called X-ray crystallography to zero in on the binding site. 

They locked the virus and the antibodies into place together - or crystallized them - and visualized the adjacent structures by bouncing X-rays off them.

The two most protective antibodies bound to the same region of the viral envelope protein that covers the surface of the virus. 

Referring to the possibility of making a vaccine from an engineered viral protein rather than the whole virus, Professor Fremont said: 'We think that this piece of the viral envelope protein alone would be able to elicit a protective immune response to Zika.'

He said vaccines made from live weakened viruses are common and effective, but can't be given to pregnant women. 

Pregnancy suppresses a woman's immune system, so a weak virus that safely immunizes most people could make pregnant women ill.

In the case of Zika - where viral infection of pregnant women can cause devastating birth defects or miscarriage - a live-virus vaccine would be unusable, but a protein-based vaccine could be a lifesaver.

The researchers said the antibodies - which protected mice from a lethal dose of Zika in the study - could also potentially be used to treat high-risk patients, such as people with other medical conditions and pregnant women.

But since the antibodies in the study were obtained from mice, they would need to be modified to be more like human antibodies, before they could be used in people.

The researchers also warned that low levels of anti-Zika antibodies - too low to protect against disease - helped the related dengue virus infect cells in a petri dish.

They said people with dengue virus tend to get sicker the second time they are infected, because low levels of antibodies left over from the first infection help the virus invade.

Dengue and Zika are both circulating in tropical parts of the Americas, including Brazil.

The researchers said that it's possible that people who get infected with dengue after Zika - or after immunization with a Zika vaccine - would develop more severe dengue disease.  

But the dengue virus could also offer a cure for Zika, according to a study by the University of North Carolina. 

The study, published in mBio, looked at antibodies produced by survivors of dengue fever and its effect on the Zika virus. 

The technology currently exists to extract these antibodies and provide them to people who may be exposed to Zika now. 

'In essence, a therapeutic treatment using antibodies derived from selected Dengue and Zika virus survivors would protect pregnant women and others from contracting the Zika virus if they came in contact with it,' said the study's principal investigator, Ralph Baric, professor of epidemiology at the University of North Carolina's Gillings School of Global Public Health.

Going forward, the researchers said additional testing would allow further refinement of the therapeutic treatment to combat the inevitable mutations of the Zika virus that will develop as more outbreaks occur.

'Best next steps would be to assess antibody-mediated protection of the developing fetus in a small animal pregnancy model, study the structure of the antibody bound to the Zika virus and see if the ultimate mutations of the virus are weakened by the therapeutic treatment, as well,' Jesica Swanstrom, a postdoctoral researcher, said.