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ver the past year, the Centers for Disease Control and Prevention took the extraordinary step of urging pregnant women to avoid travel to dozens of mainly Latin American countries to stave off infection with the Zika virus. With inclement weather prompting Americans to muse about winter vacations in sunny climes, the CDC wants to make it clear: That recommendation still stands.

CDC Director Tom Frieden admitted he is worried that people may think the worst of Zika is over and that they can let down their guard.

“We do want to emphasize that this will be the new normal until there’s a [Zika] vaccine. That if you’re pregnant, you should not go to a place where Zika is spreading,” Frieden told STAT in a year-end interview on the agency’s Zika response.

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“I think there’s a misconception that Zika is either over or was never a serious problem. It’s a devastating problem for families and individuals.”

The Zika outbreak has been an extraordinarily taxing one for the CDC, Frieden noted, leading to a number of firsts for the agency.

One notable first came on Jan. 15, when the CDC advised pregnant women to avoid 13 Latin American countries as well as a part of the United States, Puerto Rico, to avoid infection with the Zika virus.

The recommendation was made several months before the CDC and the World Health Organization concluded there was enough scientific evidence to say that Zika infection in pregnancy was causing microcephaly — abnormally small heads and often under-developed brains — in newborns. But as early as January the agency felt certain the risk was too great to wait for definitive proof; it needed to warn pregnant women.

“That may have been the single most important thing we did,” Frieden said.

The public’s take on Zika has been mixed, with many people dismissing it as an overblown problem. That contributes to the CDC’s concern that the lure of the beaches of the Caribbean and Central America might entice some US travelers this winter who ought to stay away.

But Frieden said that pregnant women, as a group, are more finely attuned to health messaging and more likely to follow advice.

Still, women often don’t know for weeks after conception that they are pregnant. And couples that may not have plans to conceive may end up doing so on a vacation. Infection in the first trimester of pregnancy appears to carry the highest risk of brain-related birth defects.

Some people may feel the risk of infection is low, Frieden acknowledged.

“It’s obviously a rare event, but the problem is it’s a devastating event,” he said. “It’s a life-changing event.”

The CDC’s Zika response to Zika has involved over 2,200 staff from across the agency’s many centers, drawing in experts on infectious diseases, birth defects, reproductive health, mosquito control, and sexually transmitted diseases.

They have rushed to do the studies that have firmed up the link between Zika infection and birth defects and with Guillain-Barré syndrome, a form of progressive paralysis that usually subsides. They have also developed tests to detect Zika infection, participated in about two dozen epidemiological investigations, and written more than 230 scientific articles and guidance documents for the public, physicians, state health departments, and the like.

The agency also established a registry to track the pregnancies of women who were infected, another first.

To date, the United States has recorded 39 pregnancies affected by Zika: 34 babies have been born with Zika-induced birth defects, and in five cases, birth defects are known to have been present but the pregnancy ended with either a miscarriage, a stillbirth or a termination.

CDC scientists acknowledge that these numbers may be an underestimate because it is hard to track pregnancies that end in abortion. If a woman learned she was carrying a fetus with Zika-related birth defects and she decided to terminate that pregnancy, the case might not be recorded in the CDC’s Zika pregnancy registry.

The latest update of findings from the registry for the 50 US states suggests that at least 1,246 pregnant women have been infected with Zika, and at least 824 of those pregnancies have come to term or have ended.

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