The World Health Organization declared the Zika virus and its suspected link to birth defects an international public health emergency Monday, a rare move that signals the seriousness of the outbreak and gives countries powerful new tools to fight it.
An outbreak of the Zika virus, which is transmitted by mosquitoes, was detected in Brazil in May and has since moved into more than 20 countries in Latin America. The main worry is over the virus' possible link to microcephaly, a condition that causes babies to be born with brain damage and unusually small heads. Reported cases of microcephaly are rising sharply in Brazil, ground zero for the disease, though researchers have yet to establish a direct link.
At a news conference in Geneva, Dr. Margaret Chan, director general of the WHO, said that clusters of microcephaly in regions with Zika cases "constitute an extraordinary event and a public health threat to other parts of the world."
She added that an "international response is needed to minimize the threat in infected countries and reduce risk of international spread." Chan said case control studies on the connection between Zika and microcephaly will start in the next two weeks.
The official "emergency" designation can trigger action and funding from governments and nonprofits around the world. It elevates the WHO to the position of global coordinator, and gives its decisions the force of international law. The agency is trying to cast itself as a global leader to revive its reputation after a faltering response during the Ebola epidemic in West Africa.
"Can you imagine if we do not do all this work now and wait until all these scientific evidence come out, people will say why didn't you take action?" Chan said.
The current outbreak of Zika has taken the world by surprise. It was first identified in 1947 in Uganda, and for years lived mostly in monkeys. But in May in Brazil, cases began increasing drastically. The WHO has estimated that 4 million people could be infected by the end of the year. It is spreading fast in the Americas because people there have not developed immunity.
The WHO has declared a public health emergency three times since 2007, when it first established the procedure — for the influenza panademic in 2009; in 2014 when polio seemed resurgent; and in August 2014 for Ebola. Some experts applauded the decision to add Zika to the list.
"This should be a global wake-up call," said Lawrence O. Gostin, director of the O'Neill Institute for National and Global Health Law at Georgetown University. But he added: "The main question on my mind is whether they will back up their words with decisive action."
Zika's rapid rise and the specter of associated birth defects have major implications in a warm region with struggling economies and vast flows of tourists. Brazil is preparing to host the Olympics this summer, and Zika is complicating those plans. The Centers for Disease Control and Prevention has advised pregnant Americans to avoid travel to the region.
Still, U.S. officials have taken pains to underscore that the virus does not pose a major threat to the United States, where mosquito control efforts are robust and effective.
But now that an emergency has been declared, the WHO can issue global travel advisories, and crucially, coordinate global efforts to combat the mosquitoes that spread Zika, a role that is badly needed as mosquito populations are fluid and know no boundaries. The agency will also help coordinate surveillance efforts, including tracking and tallying cases of Zika and microcephaly.
The last time the WHO declared a public health emergency was when Ebola was tearing through West Africa. But the agency was strongly criticized for weighing in very late, and many global health experts said it was unlikely that the agency's director, Chan, would let that happen again.
"The WHO took a very serious hit to their reputation," said Dr. Ron Waldman, a professor of global health at the Milken School of Public Health at George Washington University. "They do have to be mindful of the politics, but they have to get the science right, too. They don't have much room for slip-ups."
Zika and Ebola are very different. Ebola was incredibly deadly, and it spread through contact with bodily fluids. Zika is not known to be fatal, and it has mild symptoms for most people. So far, the evidence is inconclusive that the virus is the cause of the birth defects, so some health officials had been cautious about drawing too dire a picture.