WASHINGTON (AP) — More federal money finally is available to fight Zika, and one critical research question is how long to monitor the health of babies born to infected mothers.

Brazilian doctors have counted a small number of babies who at birth had a normal-sized head — apparently escaping Zika’s hallmark birth defect — and only later were found to have health problems.

One researcher says that defect, microcephaly, is only the tip of the iceberg.

A study is underway to help answer how big a risk babies face, and how to monitor them. But more research is needed.

Congress last week passed a budget bill that includes $1.1 billion for additional Zika research and prevention. The money comes months after the Obama administration had requested it.