Following the publication of CDC’s paper evaluating the evidence for a causal link between Zika virus and microcephaly this week, twitter was alight with pronouncements that this link has been definitively established, at least based on the CDC authors’ interpretation of Shepard’s criteria for teratogenicity and Bradford Hill’s causal considerations. That a causal link has been announced may not come as a surprise to many. Its importance is perhaps more strategic and political than scientific; the announcement will help mobilize funds and resources for control, research and management of Zika-related disease burden. But it is merely the beginning – there is still much uncertainty regarding the risk of microcephaly, other congenital abnormalities and neurological complications among Zika-infected patients, and much about the apparent geographic differences in Zika-related complications that have yet to be understood.