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When neonatal intensive care units in northeastern Brazilian hospitals started to fill up with babies with misshapen and abnormally small heads in late 2015, the first question everyone wanted answered was: What is causing this?

As pictures of the babies started circulating around the world, a second question quickly followed: What would life be like for these infants?

Within a few months, the international scientific community concluded that Zika virus infection in pregnancy, especially in the first trimester, could trigger devastating brain destruction in a developing fetus. Zika congenital syndrome, as it is now called, can manifest itself in profound ways — a cratered skull, whole sections of brain tissue missing — or subtler deficits such as hearing loss and vision problems.

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In the months since these babies began to be born, their families and the medical professionals treating them have been charting the progress of the survivors. For some, there is hope that brain plasticity — neuronal workarounds — will limit the damage. For others, development goals may not just be delayed, but missed entirely.

Read more: Another night in the hospital: the unrelenting struggle of raising Brazil’s Zika babies

To date, Brazil has confirmed Zika-related birth defects in more than 2,600 babies; another 3,200 suspected cases are still being investigated.

STAT recently revisited two affected babies and their families. Maria Eduarda Pereira — known as Duda — was one of the first Zika infants born in Recife; she is now nearly 18 months old. Dr. Regina Coeli, of the Oswaldo Cruz University Hospital there, measures what would be small milestones for other children — learning to swallow, sitting up with support — as big gains for Duda.

“I would say Duda was one of the worse cases I have cared for,” said Coeli, who said the little girl was in and out of hospital for the first nine months of her life. “Even so, she has shown great development that you might have thought impossible for a child with that level of brain damage, so that spectrum can change throughout time.”

Eduarda Alves’s daughter Sophia recently celebrated her first birthday. Like Duda and many other babies with Zika congenital syndrome, Sophia’s vision has been affected. Still, she’s learning and developing. Sophia can’t yet sit up by herself, but can hold herself in a sitting position if placed in one, and can stand if supported.

Said Alves: “We’re going at her pace.”