WASHINGTON, United States (AFP) – US researchers have identified antibodies in lab mice that may be able to prevent infection with the mosquito-borne Zika virus, in what they described Wednesday as a “significant step” toward a vaccine.

The team at Washington University School of Medicine in St Louis published their findings in the journal Cell.

The research shows how these six antibodies interact with the virus, and that they are specific enough to Zika virus — and not other viruses — that they could be used in diagnostic tests, the researchers said.

“Importantly, some of our antibodies are able to neutralize African, Asian and American strains of Zika virus to about the same degree,” said co-senior author Daved Fremont, professor of pathology and immunology.

However, further research on vaccinating mice is not likely to be helpful, since mice obtain their mothers’ antibodies mostly after birth.

In pregnant women, the mother’s protective antibodies cross directly from the placenta to the fetus.

Finding a way to vaccinate pregnant women is key because Zika can cause birth defects.

Unlike most people, pregnant women cannot receive vaccines made from live, weakened viruses because pregnancy suppresses a woman’s immune system and the small amount of virus could make the expectant mother ill.

The antibodies will have to be adapted and vaccine trials will likely need to be done in primates before they can be tested in people.

There is no vaccine on the market to prevent Zika, a virus that first emerged in 1947 in Uganda but in recent years has exploded across Central and South America and the Caribbean region.

Experts say the race to craft a vaccine is likely to take years.