European scientists announced Thursday they had discovered antibodies which attack Zika, a step they hope will pave the way for a protective vaccine against the brain-damaging virus.
The antibodies -- frontline soldiers in the immune system -- "efficiently neutralise" Zika in human cells in lab dishes, and are also effective against its cousin virus dengue, the team reported.
The discovery "could lead to the development of a universal vaccine" against both diseases, they hoped.
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The Zika-zapping molecules were obtained from people who had previously been infected with dengue and whose immune systems had produced antibodies to fight that disease.
"The antibodies could be used, for example, to protect pregnant women at risk of contracting the Zika virus," said Felix Rey, a virology expert at France's Institut Pasteur who co-authored twin studies in Nature and Nature Immunology.
"We never expected to discover that the dengue virus and the Zika virus are so close that some antibodies produced against the dengue virus could also neutralise the Zika virus so potently," he added.
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But Rey cautioned that a working vaccine is likely far off.
"There is a lot still to be done, notably to conduct a clinical trial. This may take some time."
Benign in most people, Zika has been linked to a form of severe brain damage, called microcephaly, in babies, and to rare adult-onset neurological problems such as Guillain-Barre Syndrome, which can result in paralysis and death.
In an outbreak that started last year, about 1.5 million people have been infected with Zika in Brazil, out of a global total of some two million, and more than 1,600 babies born with abnormally small heads and brains.
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