Zika virus 'spreading explosively,' WHO leader says

(CNN)The Zika virus is "is now spreading explosively" in the Americas, the head of the World Health Organization said Thursday, with another official estimating between 3 million to 4 million infections in the region over a 12-month period.

"The level of concern is high, as is the level of uncertainty," Dr. Margaret Chan, WHO's director-general, told her organization's executive board members. "We need to get some answers quickly."