Health officials have dismissed calls for this summer's Rio Olympics to be postponed or moved over the Zika crisis.
With just 10 weeks before the Games are due to begin, 152 leading scientists have written an open letter to the World Health Organisation (WHO) saying new findings about the virus make staging the event in the city "irresponsible" and "unethical".
But the WHO rejected the warning, insisting that shifting the Olympics would "not significantly alter" the spread of the virus.
It said in a statement: "Based on current assessment, cancelling or changing the location of the 2016 Olympics will not significantly alter the international spread of Zika virus.
"Brazil is one of almost 60 countries and territories which to-date report continuing transmission of Zika by mosquitoes. People continue to travel between these countries and territories for a variety of reasons.
"The best way to reduce risk of disease is to follow public health travel advice."
One of the letter's signatories, Professor Arthur Caplan, told Sky News a postponement of three to six months would have allowed time for a vaccine to be created.
He added: "What we are learning about Zika is that the strain not only causes birth defects but also has this neurological explosion impact on children. It's more serious than we thought.
"We are also starting to understand that it can cause paralysis, rarely but it can do it, in adults, and we don't yet know how long it lingers in a person.
"To top it all off Brazil has been undergoing economic and political troubles and it's not clear that they're going to be able to do what's necessary to protect both athletes and visitors."
Zika can cause microcephaly in which babies are born with unusually small heads and brains.
It has also been linked to Guillain-Barre syndrome and Acute Disseminated Encephalomyelitis which affect the nervous system.
Nearly 1,300 babies have been born in Brazil with microcephaly since the mosquito-borne Zika began circulating there last year.
The letter said the Games should be moved or delayed "in the name of public health" after infections in Rio rose despite increased efforts to wipe out the mosquitoes.
Signatories were from more than two dozen countries and include former White House science adviser Dr Philip Rubin.
The WHO has already advised pregnant women not to go to Rio and says travellers should avoid poor and overcrowded parts of the city.
The UN agency also predicts the Zika risk will drop in August, with the South American winter resulting in fewer mosquitoes.
No Olympic Games has ever been moved from its host city due to medical concerns.
A dissenting voice in the scientific community is Dr Tom Frieden, director of the US Centers for Disease Control and Prevention.
He said: "There is no public health reason to cancel or delay the Olympics.
"The risk to delegations going and athletes is not zero, but the risk of any travel isn't zero. The risk is not particularly high other than for pregnant women."