As many as one in seven infants whose mothers were exposed to the Zika virus during pregnancy later developed health problems, according to a new study.
Researchers at the US Centers for Disease Control and Prevention who conducted the study said it was the first to follow such a large sample of children exposed to the virus after their birth.
“What makes this report unique, is we’re looking at the health of these babies beyond what was observed at birth,” said Peggy Honein, the director of congenital and developmental disorders at the US Centers for Disease Control and Prevention (CDC).
“This is really providing us with the first clues about how common some of these neuro-developmental disabilities might be in an entire cohort of children who are impacted by Zika during pregnancy,” said Honein.
Zika became widely associated with the birth defect microcephaly in the winter of 2016, after the birth defect showed up in Brazil with alarming frequency. Zika is a mosquito-borne disease transmitted by the Aedes Aegypti mosquito, a species especially suited to living near people.
Soon after, researchers started tracking pregnant women infected in the United States, and built a database called the US Zika Pregnancy and Infant Registry. About 7,300 pregnancies have been followed to date, including 4,800 reported from US territories and freely associated states.
The study released this week looked specifically at those 4,800 pregnancies, and included women diagnosed with Zika in American Samoa, Micronesia, Marshall Islands and the especially hard-hit Puerto Rico and US Virgin Islands.
Of those 4,800 pregnancies, 1,450 infants received enough follow-up care to be included in the study, and were one year old by February 2018 (the study’s cutoff). Researchers found 14% of these infants had a Zika-associated birth defect, a neuro-developmental abnormality possibly associated with Zika, or both.
Among those with birth defects, 6% had eye abnormalities, brain anomalies or microcephaly, a condition in which an infant’s head and brain are significantly smaller than usual. Before Zika was present in these areas, eye and brain birth defects impacted just 0.16% of infants, suggesting Zika-impacted babies are 30 times more likely to experience these defects.
An additional 9% of babies had neuro-developmental abnormalities, including hearing problems, seizures, too much or too little muscle tone, involuntary muscle movements or cerebral palsy, difficulty swallowing, visual impairments or late onset microcephaly.
In all cases, researchers said tracking the families was difficult. Many of those cases were in Puerto Rico and the US Virgin Islands. Zika transmission was widespread in these areas in 2016, and the outbreak was followed quickly by Hurricane Maria, which displaced many families.
As a result, the 1,450 babies followed by researchers represent only two-thirds of all those who were eligible to be in the study. The remainder did not receive the follow-up care suggested for children exposed to Zika during pregnancy.
“We know all of these children regardless of the cause of the neurodevelopmental disorder need referrals,” said Honein. “It really emphasizes that the Zika story is not over.”
Local Zika transmission is still ongoing in Puerto Rico, which has struggled to recover from Maria following a bungled federal disaster response. In 2018, 74 cases of Zika have been reported in US territories, nearly all of which are in Puerto Rico.
Researchers recommended women who live in areas with endemic Zika should take steps to try to avoid mosquito bites, such as putting screens on windows, wearing repellant and use mosquito nets at night. Because Zika can be sexually transmitted, the CDC also recommended men abstain from sex for three months if they believe they have been exposed.
The National Institutes of Health is developing several Zika vaccines, which were expected to enter phase two or phase three trials by 2018.