The World Health Organization designated the Zika virus a public health emergency of international concern Monday, an action it has taken only three times before and which paves the way for the mobilization of more funding and manpower to fight the mosquito-born pathogen spreading “explosively” through the Americas. Zika, which was first identified more than 50 years ago, has alarmed public health officials in recent months because of its possible association with thousands of cases of brain defects, known as microcephaly, in newborns.

The WHO has estimated that the virus will reach most of the hemisphere and infect up to 4 million people by year’s end. Margaret Chan, WHO director-general, said at a press briefing that the primary reason for the decision was that members of an 18-member advisory panel agree that a causal relationship between Zika and microcephaly is “strongly suspected” although it hasn’t been scientifically proven. She said that given the seriousness of the conditions being reported, the consequences of waiting were too great. FULL REPORT