Early results from a crucial case-control study in Brazil have confirmed a direct causal link between Zika virus infection in pregnant women and the brain damaging birth defect microcephaly in their babies.
But while preliminary findings from the first 32 cases involved in the study confirm causality, the researchers said, the true size of the effect will become clear only after full analysis of all 200 cases and 400 controls.
The study, published in The Lancet Infectious Diseases journal on Thursday, was requested by the Brazilian health ministry to investigate the causes of the microcephaly epidemic that the World Health Organisation (WHO) declared an international public health emergency earlier this year.
The outbreak of Zika, a mosquito-borne disease, was detected last year in Brazil, where it has been linked to more than 1,700 cases of microcephaly, a birth defect marked by small head size that can lead to severe developmental problems.
The virus has since spread rapidly through the Americas and Caribbean.
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While the WHO and other disease experts had said there was strong scientific consensus that Zika and microcephaly were linked, evidence until now has been largely circumstantial.
