Most toddlers who were exposed to Zika in the womb and born with birth defects still suffer from many long-term problems at age two, according to the first report characterizing the longer-term health effects of prenatal exposure to the virus. These children often continue to have seizures as well as an inability to respond to noises in their surroundings or follow objects with their eyes, researchers found.

The findings are based on follow-up exams of Brazilian kids born with smaller than normal heads, a birth defect called microcephaly. Earlier analyses suggested such infants would have serious developmental delays, but the new report, released Thursday by Brazilian and U.S. health officials, is the first to provide a detailed account of what challenges these kids will face as they grow up—and to confirm children born with Zika-related microcephaly will probably need lifelong care.

The report comes from careful tracking of 19 babies born in 2015 and 2016 who were diagnosed with microcephaly and had accompanying laboratory evidence of congenital Zika virus. The children were all from northeastern Brazil, and the study found that at around ages 19 to 24 months the toddlers had conditions including an inability to sit independently, difficulties with sleeping and feeding, seizures, and hearing and vision problems. About 75 percent of them suffered from cerebral palsy. And the majority of the kids—three quarters—suffered from at least three of these issues. These children “have severe functional limitations and will require specialized care from clinicians and caregivers as they age,” the study says. Ten of the subjects were male and nine were female.

Brazilian authorities produced the analysis in collaboration with the U.S. Centers for Disease Control and Prevention and published it Thursday in the CDC’s Morbidity and Mortality Weekly Report. Health authorities say the new findings will help shape how countries should prepare for the years ahead, and will underscore the importance of continuing to monitor children severely affected by the virus. “The findings may not be representative of all the babies whose mothers got exposed to Zika during pregnancy,” cautions Albert Ko, a Zika expert and professor of epidemiology and medicine at Yale University who was not involved in the study. “These cases are likely to be the worst of the worst because 70 to 80 percent of these kids had severe microcephaly—meaning their heads were more than three standard deviations smaller than the average infant head. The big remaining question is: How about all the babies that didn’t have this severe presentation?” he says.

More developmental updates will be released in the coming years from Brazil and elsewhere. As of September 2017 almost 3,000 newborns had reportedly been born with microcephaly in Brazil, and 2,959 of them are being closely monitored. In the U.S. the latest numbers suggest more than 2,000 Zika-infected women have had babies. At least 98 of them were born with Zika-related birth defects; another 142 infants were born with such issues in the U.S. territories, where the virus has been much more common.

The 19 children included in this particular study were part of a case-control investigation from selected areas of Brazil’s Paraíba State. One possible limitation of the findings, the study authors wrote,  is that these infants had their blood collected between one and seven months after birth—so it is possible some of them might have been infected with Zika after they were born, not in the womb.

The study authors also cautioned the picture may be worse than they found; even though four of the 19 children appeared to be showing more typical development, that could be because they were misdiagnosed as having microcephaly or mistakenly found to have congenital Zika syndrome due to passive transfer of maternal antibodies when they actually were not infected.