“It’s heartbreaking,” the C.D.C. director, Dr. Brenda Fitzgerald, said in an interview. “We would expect that these children are going to require enormous amounts of work and require enormous amounts of care.”

The new study, conducted with the Brazilian Ministry of Health and other organizations, evaluated children in Paraíba state, part of Brazil’s northeastern region, which became the epicenter of the Zika crisis. The researchers initially studied 278 babies born in Paraíba between October 2015 and the end of January 2016. Of those, 122 families agreed to participate in follow-up evaluations this year. The study released Thursday involves what were considered the most severe of those cases, Dr. Peacock said.

The children were evaluated when they were between 19 and 24 months old. Four of the 19 evaluated had very few symptoms or developmental difficulties, and researchers concluded they were “misclassified” as Zika babies, possibly because of errors in lab testing or head measurement.

But 15 children, eight girls and seven boys, had a range of symptoms, most of which had not improved since infancy. All had severely impaired motor skills, with all but one child meeting the conditions for a diagnosis of cerebral palsy. Most had seizures and sleeping problems. Eight had been hospitalized at some point, most for bronchitis or pneumonia. Nine had difficulty eating or swallowing, which can be life-threatening because food can get stuck in the lungs or the children can be malnourished.

Most had vision and hearing problems serious enough to impede their ability to learn and develop, Dr. Peacock said. “Children wouldn’t turn to the sound of a rattle or they wouldn’t be able to follow an object, which typically a child can do by six to eight weeks of age,” she said. “What we suspect is that because they have experienced so much damage to the brain, that connection of an object being presented and being transmitted to the back of the brain is not happening, so that is a significant cognitive impairment.”