WASHINGTON — Babies who at first seem to have escaped the Zika virus’ devastating hallmark defect – an abnormally small head at birth – might not be free of problems, after all.

Brazilian doctors have counted a small number of babies who at birth had a normal-sized head and only later were found to have delayed neurodevelopment. At 5 months, one could use one hand but not the other. Later, some even developed that defect, called microcephaly. The brain and skull weren’t growing properly after birth, instead of before.

“Microcephaly is only the tip of the iceberg, only the thing we see when the baby is born,” Dr. Vanessa Van der Linden, a pediatric neurologist in Recife, Brazil, told a meeting at the National Institutes of Health, where she outlined a long list of Zika-related abnormalities.

Children’s health experts say intense study is needed of babies born to Zika-infected mothers to learn the range of health problems they may face.

“It is just critical to evaluate the entire child. Even in the child who does not have microcephaly, that doesn’t mean no evaluation is needed,” said Dr. Catherine Spong of the NIH’s National Institute of Child Health and Human Development, which despite budget constraints has begun research to better understand the risk to babies.

After months of partisan bickering, Congress last week passed a budget bill that includes $1.1 billion to address the Zika crisis.

While mosquito season is winding down in parts of this country, Zika’s threat here and abroad is not diminishing, and that’s why health officials say a sustained commitment is vital.