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The Zika outbreak may no longer be a global health emergency, but the need for answers about the virus remains pressing, a range of experts said Tuesday as a new study underscored the risk Zika poses to babies exposed in the womb.

The study, from scientists in Brazil and at the Centers for Disease Control and Prevention, assessed the health of 13 babies who were infected before birth.


All were born with normal head sizes but in the months after birth, 11 were diagnosed with microcephaly, the stunted brain condition that first brought Zika to international attention.

Other symptoms that signal Zika-related brain birth defects were recorded in the group. For instance, seven had epilepsy and 10 had difficulty swallowing.

Elsewhere recent studies, including one published this week, have shown Zika damages the testicles of infected mice, raising questions about whether infection might have an impact on the fertility of men who contract the virus.


These and other questions need to be answered, the World Health Organization said Tuesday during a news briefing, after a meeting to discuss Zika research priorities with affected countries.

Studies underway to chart how long Zika virus is found in body fluids will need to be expanded to look to see if the damage seen in mice is mirrored in men, said Dr. Nathalie Broutet, a reproductive health expert and coordinator of Zika research for WHO.

“We are following up for one year. If we can — and I think we should do that — follow up these men for more than two years and maybe 10 years … so that we can really understand better the long-term impact of this infection,” she said.

The WHO announced Friday that it no longer deems the Zika outbreak to be a global health emergency.

But Dr. Peter Salama, who heads the agency’s emergencies program, said the move doesn’t signal a waning of concern about Zika. Rather, he said, it reflects the fact that the virus and the disturbing birth defects it can trigger represent “a significant and enduring public health challenge.”

Many crucial questions remain to be answered, Salama said. Key among the questions: Why has Brazil recorded so many cases of Zika birth defects when other affected countries have reported so few? The WHO reports weekly on Zika microcephaly cases, which now total about 2,300 worldwide. But Brazil accounts for about 92 percent of the cases, and the lion’s share of the cases comes from the northeast of that country.

Scott Weaver, an expert on viruses that are spread by mosquitoes, finds the discrepancy puzzling.

“To be honest, I’ve thought a lot about this, I’ve talked to a lot of people about it and I haven’t heard a very satisfying explanation [for it],” said Weaver, director of the Institute for Human Infections and Immunity at the University of Texas Medical Branch in Galveston.

Still, he believes it is starting to appear that the rate of Zika-related microcephaly cases outside of Brazil may be lower than what that country has reported.

“I’ll be surprised if the incidence in Colombia and Puerto Rico and other places ends up being as high as northeast Brazil,” Weaver said.

CDC Director Dr. Tom Frieden, who remains very concerned about Zika, does not share that view.

Frieden said he is skeptical about the suggestion that Zika took a higher toll in northeastern Brazil, saying evidence from a number of places — including CDC data that haven’t yet been published — paint a consistent picture. He theorized that Brazil has recorded higher numbers of cases because it has looked harder than other countries and because its outbreak started sooner.

“So I think if people are hoping that this will be something idiosyncratic about that part of the world, that’s very unlikely to be the case from our perspective,” Frieden told STAT.

Frieden and Weaver agreed, though, on some of the Zika research priorities, including the need for better tests to figure out, after the fact, who has been infected with Zika and whether infection confers immunity.

Existing tests cannot distinguish Zika antibodies from those generated after a bout of dengue fever, except soon after infection. So while experts would like to know whether people in Asia and Africa are vulnerable to Zika or already mostly immune, they currently have no way to answer that question.

Frieden and Weaver also agreed that people should not misinterpret the meaning of WHO’s decision to end the Zika global health emergency.

“I think the risk is there are a lot of people who will just read the headlines and … some of them will mistakenly assume: ‘OK, it’s safe now to travel wherever I want to go, even if I’m pregnant, even if I’m the partner of a pregnant women,’” Weaver said.

That is not the message the CDC wants people to hear, said Frieden, who stressed that pregnant women should continue to avoid travel to places where Zika is circulating.

And women who contracted Zika during a pregnancy should have their baby’s development monitored, even if he or she appeared healthy and symptom-free at birth. That’s a lesson from the new study, Frieden said.