CDC confirms Zika causes microcephaly

Scientists at the Centers for Disease Control and Prevention (CDC) now say the Zika virus definitely causes severe birth defects, including eye abnormalities.

“We’ve now confirmed what mounting evidence has suggested, affirming our early guidance to pregnant women and their partners to take steps to avoid Zika infection and to health care professionals who are talking to patients every day,” said Tom Frieden, MD, MPH, director of the CDC. “We are working to do everything possible to protect the American public.” 

In a special report published this week in the New England Journal of Medicine, CDC officials describe a rigorous evaluation of evidence using Shepard's criteria, concluding that the evidence shows causation due to the "unlikelihood of the two rare events occurring together.”

Prior to this study, most experts were careful to avoid characterizing the relationship between Zika virus and microcephaly as causal, describing the link as "a strong association."

“This study marks a turning point in the Zika outbreak,” Frieden said. “We are also launching further studies to determine whether children who have microcephaly born to mothers infected by the Zika virus is the tip of the iceberg of what we could see in damaging effects on the brain and other developmental problems.”

“My hope is that now that we can be more convincing that Zika virus does cause these severe birth defects in babies, that people will focus on our prevention messages more carefully,” said Sonja A. Rasmussen, MD, lead author of the study and director of the division of public health information dissemination at the CDC.