Back in 2015, Brazil reported a horrific a surge in birth defects. Thousands of babies were born with brain damage and abnormally small heads, a condition called microcephaly.
Scientists quickly concluded the Zika virus was the culprit. So when Zika returned last year during Brazil's summer months of December, January and February — when mosquitoes are most active — health officials expected another surge in microcephaly cases.
But that never happened.