By: Alanna Shaikh, MPH on April 15, 2016 Yesterday, the US Centers for Disease Control and Prevention (CDC) published an article that confirmed Zika virus causes microcephaly, a neurological disorder in which babies are born with abnormally small heads. We’ve been hearing about the link between Zika and microcephaly for the last five months, but this is a new level of evidence. Last fall, Brazil saw both a rapid increase in the number of babies born with microcephaly and its first indigenous outbreak of Zika virus. Then, in November Brazilian public health authorities found Zika virus in the blood of an infant born with microcephaly. That was a strong correlation, but not a link. At that point, it was still possible that pregnant women exposed to Zika also tended to be exposed to something that causes microcephaly. The CDC article, published in the New England Journal of Medicine, establishes a new level of certainty. It reviews all the current evidence on Zika virus and pregnancy. This includes factors such as exactly what kind of brain damage is associated with Zika infection and the biological mechanism through which Zika could cause microcephaly. Based on this evidence, they state that “a causal relationship exists between prenatal Zika virus infection and microcephaly and other serious brain anomalies.” This is pretty much as certain as medical research gets. Therefore, we can now say that Zika causes microcephaly, not just that it appears to be linked or is associated with it. Zika is not a suspect any more. It has been tried and convicted. A screengrab from CDC.Gov The results are useful for medical research; they open up new avenues from estimating risks and identifying the impacts of Zika infection. They do not, however, have much impact from a public health perspective. Health authorities were already operating from a position of caution and assuming that Zika causes microcephaly. On February 1, the World Health Organization declared the Zika-Microcephaly link a “public health emergency of international concern” which kicked into gear an international emergency response mechanism. Meanwhile, women in Zika-prevalent areas have been advised to avoid pregnancy at this time, and pregnant women have been advised against travel to these areas. Zika virus, and the research we’ve seen on it is an excellent example of what public health systems look like when they work. Zika virus has been seen for a long time in Africa, but never in a country with a public health system that had the surveillance capacity to track it and find linkages to things like birth defects. Brazil did have that capacity, and they identified a link and asked the CDC to assist them in researching the virus. It was that research which brought us this definitive link. Now that we have come this far, though, we’re at a stopping point. If we’re going to do more research into the virus, and find ways to treat and prevent it, we need a financial commitment. And here, the United States Congress has not been as pro-active as it could be. The White House has asked congress to approve $1.9 in Zika response funding. Congress has so far refused, though it did approve a measure that might allow for the fast track of Zika-related research at the Food and Drug Administration. But that measure did not include any new funding. Instead, the White House was forced to shift $589 million from ebola response to Zika preparedness. Zika virus isn’t going to go away without a global financial and logistical commitment to stopping it. It was true when we suspected a link with birth defects and it remains true with a link that’s certain.