American scientists studying the Zika virus have warned that it could be a decade before a vaccine is publicly available.
The virus is linked to shrunken brains in unborn children, leading to severe brain damage or death.
It has spread to more than 20 countries, and has caused panic in Brazil where thousands of people have been infected.
There is currently no vaccine or cure, and diagnostic testing is difficult.
The search for a vaccine is being led by scientists at the University of Texas Medical Branch.
They have visited Brazil to carry out research and collect samples, and are now analysing them in a suite of high-security laboratories in Galveston.
But they warn that although a vaccine could be ready for testing in two years, it may be another decade for it to be approved by regulators.
Access to the building is tightly controlled by police and the FBI.
Speaking to the BBC inside the facility, Professor Scott Weaver, director of the Institute for Human Infections and Immunity, said people were right to be frightened by the virus.
"It's certainly a very significant risk," he said, "and if infection of the foetus does occur and microcephaly develops we have no ability to alter the outcome of that very bad disease which is sometimes fatal or leaves children mentally incapacitated for the remainder of their life".
The Zika virus was discovered in monkeys in 1947 in Uganda's Zika Forest, with the first human case registered in Nigeria in 1954 but for decades it did not appear to pose much of a threat to people and was largely ignored by the scientific community.
It was only with an outbreak on the Micronesian island of Yap in 2007 that some researchers began to take an interest.
In the past year the virus "exploded" said Prof Weaver, sweeping through the Caribbean and Latin America "infecting probably a couple of million people".
The symptoms in adults and children are similar to those for dengue fever but generally milder, including flu-like aches, inflammation of the eyes, joint pain and rashes although some people have no symptoms at all.
In rare cases the disease may also lead to complications including Guillain-Barre syndrome, a disorder of the nervous system which can cause paralysis.
There is some evidence that Zika can be transmitted through saliva and semen although this does not appear to be common.
"We think that sexual transmission can occur but we don't know how often or what the risk is to an individual man who becomes infected," said Prof Weaver.
The main concern is for unborn babies and - because Zika is difficult to diagnose - it can be late in a pregnancy before expectant mothers are informed of the risk, if they are informed at all
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