After months of hesitation, U.S. health officials now say that the Zika virus is indeed the cause of severe brain damage in the infants of some women who were infected with the virus during pregnancy.
A CDC review published online Wednesday in the New England Journal of Medicine describes evidence of what U.S. health officials now call a causal relationship between the virus and a severe form of microcephaly and intracranial calcifications.
The study marks a turning point in the current Zika outbreak, says Dr. Tom Frieden, chief of the CDC. “There’s still a lot that we don’t know, he says. “But there is no longer any doubt that Zika causes microcephaly.”
A causal link between the bite of a mosquito and brain malformations is unprecedented, he says. “And it is because this was so unprecedented that we have until now waited to say that we have concluded that there is a causal link.”
There was no single smoking gun, CDC officials say. Dr. Sonja Rasmussen, editor-in-chief of CDC’s Morbidity and Mortality Weekly Report and an author on the report, says the conclusion came from looking systematically through the accumulating evidence.
The team used two approaches to confirm the link. The first method involved finding an overlap between a rare exposure and a rare defect. It was the same approach used years ago to confirm the effects of rubella on a pregnancy, and the same used to characterize fetal alcohol syndrome.