Millions at risk of contracting Zika virus
The World Health Organisation says three to four million people could be infected with the Zika virus in the Americas this year.
Most will not develop symptoms, but the virus spread by mosquitoes has been linked to brain defects in babies.
The US hopes to start vaccine trials in people by the end of the year.
The WHO says Zika has gone from a mild threat to one of alarming proportions.
Jeremy Farrar from the medical research charity, the Wellcome Trust, says he's not seen any virus have such a potentially huge impact.
"It will be difficult to develop because you're going to be targeting women - particularly pregnant women - and that's always a major challenge. We can't wait for a vaccine to come. 2016 has to be about the control of the mosquito,"he said.
An emergency team has been established after the explosive spread of the virus.
(File photo: Getty Images)