The WHO has rejected a call by 150 medical experts for the 2016 Olympic Games to be moved or postponed, saying it would not alter the spread of the zika virus.
In an open letter, 150 international scientists, doctors as well as medical ethicists from Oxford, Harvard and Yale universities said it would be unethical for the Games to go ahead due to the danger to public health.
They also said the global health body should revisit its guidance on the virus.
But the WHO said cancelling or moving the Games would not significantly alter the spread of the virus, and the International Olympic Committee also said it saw no reason to delay or move the event.
The outbreak began in Brazil a year ago, but now more than 60 countries and territories have continuing transmission.
While Zika's symptoms are mild, in the letter the experts said it caused babies to be born with abnormally small heads and could also cause a rare and sometimes fatal neurological syndrome in adults.
The letter cited the failure of a mosquito-eradication programme in Brazil, and the country's "weakened" health system as reasons to postpone or move the Olympics in "the name of public health".
"An unnecessary risk is posed when 500,000 foreign tourists from all countries attend the Games, potentially acquire that strain, and return home to places where it can become endemic," the letter says.
The biggest risk, it adds, is if athletes contract the virus and returned home to poor countries that have not yet suffered a Zika outbreak.
They also express concern the WHO has a conflict of interest because of its partnership with the IOC.
The Rio Olympics are due to take place between 5 and 21 August.
In a statement, the WHO, which has declared the Zika virus a global public health emergency, said: "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."