The data analyzed come from a registry of 1,450 children in Puerto Rico and the U.S. Virgin Islands whose mothers were confirmed through lab tests to have been exposed to Zika while pregnant. Six percent of the children suffered from birth defects such as small head size and brain and eye damage. Nine percent had at least one neurodevelopmental issue such as seizures or difficulty swallowing. And 1 percent had both.
Margaret Honein, director of the CDC’s Division of Congenital and Developmental Disorders, said in an interview that there appeared to be a wide range of outcomes, with some children more affected than others. She said that some of the children born with severe microcephaly — or a smaller-than-normal head size — do in fact have major impairments, as doctors had feared.
“We are still early in the Zika story, and we still have lot to learn about how these children will grow and develop,” she said.
The mosquito-borne virus made headlines in fall 2015 when researchers identified it as the cause of an outbreak in northeastern Brazil that resulted in a sudden increase in babies being born with abnormally small heads. Researchers were alarmed that the illness — which was previously believed to mostly produce mild symptoms such as a rash and fever — had resulted in such serious problems, and a worldwide effort was launched to investigate the disease and try to prevent further infection.
While Zika continued to spread in 2016, the number of cases of microcephaly was lower than predicted, deepening the mystery. In the New England Journal of Medicine, some researchers speculated about “the presence of some other unknown cofactor” that, combined with Zika infection, led to the more severe birth defects.
In Puerto Rico and the other U.S. territories, recent hurricanes have added significant challenges to the care and monitoring of children exposed to Zika. However, it does not seem to have resulted in a surge in Zika cases, and public health officials say they are seeing relatively low levels of transmission in that region. In 2018, in the U.S. territories, there have been a little more than 70 cases.
However, Honein said that given the historical patterns of how viruses move over time, “we expect there will be multiple outbreaks in the future” around the world.
“I think the bottom line is that the Zika story is not over,” she added. “People may feel like it's behind us. For these children, it's not over, and we need to know as much as possible so that we can be prepared” in case something similar happens again.
Indeed, researchers reported this year the first confirmed case of a Zika-exposed baby born with microcephaly from continental Africa and the possibility of two older children, ages 7 and 8, in Cambodia from an earlier outbreak.
Honein said the report published Tuesday shows that there are still “opportunities for improvement” in the screening of children who may have been exposed to Zika in utero.
“We really urge parents to get recommended care — brain images after birth, having measurements taken, getting a developmental screening and having an eye evaluation,” Honein said.
The National Institutes of Health is leading an effort to develop vaccines for Zika, but researchers are still in the testing phase.
The CDC is encouraging pregnant women to take precautions to avoid mosquito bites and to avoid travel to areas where Zika is spreading. The first trimester is possibly the most critical; studies have shown that many of the babies with the most severe birth defects were exposed during those months.
The CDC further recommends that a man who has traveled to a Zika-endemic area or is known to have been exposed to the virus should wait at least three months before trying to conceive with his partner. This is a change from previous guidelines that recommended waiting six months. New data appears to suggest that risk of infectious Zika virus in semen declines during the three months after symptoms begin.
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