The World Health Organization on Friday announced that the Zika virus outbreak, linked to deformations in babies' heads and brains, no longer poses a world public health emergency, though it warned the epidemic remains a challenge.
Brazil, the epicentre of the outbreak, has however refused to downgrade the risk, while experts swiftly lashed out against the world health body's decision.
"The Zika virus remains a highly significant and long term problem, but it is not any more a public health emergency of international concern," the world health body's emergency committee chair Dr. David Heymann said.
While Zika causes only mild symptoms in most people, pregnant women with the virus risk giving birth to babies with microcephaly -- a deformation that leads to abnormally small brains and heads.
It can also cause rare adult-onset neurological problems such as Guillain-Barre Syndrome (GBS), which can result in paralysis and even death.
In the outbreak that began in mid-2015, more than 1.5 million people have been infected with Zika, mainly in Brazil, and more than 1,600 babies have been born with microcephaly since last year, according to the WHO.
The UN's global health agency declared the Zika epidemic a global health emergency in February 2016.
Researchers earlier this year warned that at least 2.6 billion people, over a third of the global population, live in parts of Africa, Asia and the Pacific where Zika could gain a new foothold, with 1.2 billion at risk in India alone.
Brazil on Friday said it would continue to treat the outbreak as an emergency.
"We will maintain the emergency (status) in Brazil until we are completely tranquil about the situation," Health Minister Ricardo Barros told journalists.
In most cases worldwide, people have been infected with the virus by mosquitoes, though some have contracted the disease through sexual contact.
'A lot of unknowns'
The WHO was careful on Friday not to dismiss the risk still posed by the virus, which has been detected in 73 countries worldwide, mainly in Latin America and the Caribbean.
"We are not downgrading the importance of Zika, in fact by placing this as a longer term of program of work, we're sending the message that Zika is here to stay and WHO's response is here to stay in a very robust manner," said Dr. Peter Salama, director of the agency's health emergencies program.
There are still, he added, "a lot of unknowns" in the battle against Zika.
The WHO believes the "Zika virus and associated consequences remain a significant enduring public health challenge requiring intense action but no longer represent" a global health emergency, it said in a statement.
"Many aspects of this disease and associated consequences still remain to be understood, but this can best be done through sustained research," it added.
The emergency committee's head Heymann said Brazil's decision to continue dealing with the epidemic as an emergency was "appropriate", even as he affirmed the virus need not be dealt with as an emergency of international concern.
Georgetown University global health and law expert Lawrence Gostin described the WHO decision as "quite worrying", particularly since the southern hemisphere will soon enter the high-risk summer season for mosquitoes.
"I think the international response to Zika has been lethargic, and with WHO's action to call off the global emergency, it has provided reason for governments and donors to pull back even more," Gostin said.
"That is a recipe for the very lack of preparedness the world has seen time and again with infectious diseases."
Meanwhile, in Florida, the only U.S. state so far to have documented local transmission of Zika, cases continued to mount.
"Florida maintains an active public health emergency declaration in 38 counties," said the state's department of health spokeswoman Mara Gambineri.
The Zika outbreak sparked fears of infection amongst travelers and athletes taking part in this summer's Olympic Games in Brazil.
The WHO later knocked down those concerns, saying that no cases had been detected among spectators or athletes.
Two anti-Zika vaccines are currently being tested, according to the WHO. At the moment, there is no cure for Zika.