The world may be just weeks away from a viable Zika virus test, but a vaccine is still at least a year and a half away from large-scale trials, the World Health Organization said Friday.

About 15 companies and groups are involved in the race to find a vaccine for the mosquito-borne virus, though “most have only just started work,” the WHO’s Dr. Marie-Paule Kieny said at a Geneva press conference.

The WHO declined to provide details of the full list of those working on vaccine development, but a spokesperson said the list would be published in about two weeks.

The viral disease, which is associated with birth defects in the children of pregnant women who become infected, has emerged in South and Central America in recent months and is expected to spread.

Though cases have already been reported in the U.S., experts say the disease is less of a threat here than in other parts of the world.

Read: What exactly is the Zika virus, and why should you care?

And though there are two fairly advanced vaccine efforts—from the U.S. National Institutes for Health and the privately-held Indian company Bharat Biotech International Limited—it will be many months before those are ready for large-scale trials, Kieny said.

Bharat had already been working on a Zika virus vaccine, spurred by the prevalence of dengue fever and chikungungya, which are both spread by the same mosquito carriers as Zika, the company told The Wall Street Journal last week.

In the U.S., trials for a vaccine could start by late summer, though full approval would also take years, The Wall Street Journal reported Monday.

French-based pharmaceutical company Sanofi SA SAN, +0.81% is also working on a Zika virus vaccine, as is Iowa-based NewLink Genetics US:NLNK The University of Texas is involved in an effort in conjunction with Brazil’s Health Ministry.

The years-long road map for a Zika vaccine is speedy by vaccine development standards: most take at least two decades to develop.

This fast-tracking was made possible by the last such large-scale global outbreak, of Ebola, Kieny said. The WHO put special procedures in place after the 2014 outbreak to fast-track late-stage tests and vaccines.

Read: You are more likely to get these diseases than the Zika virus