As the Zika virus spreads throughout Latin America, alarm bells are blaring and questions are flying: How dangerous is this disease? Could it reach the United States and spread here? How bad would it be?

For some parts of Latin America and the Caribbean, Zika is already very, very bad. On Thursday, the World Health Organization warned that Zika was “spreading explosively” throughout the region, and millions would likely be infected this year. Earlier this week, President Obama called for rapid research on the virus, for which there is no cure or treatment. The WHO also declared a global emergency at a meeting on Monday.

As the Zika virus spreads throughout Latin America, alarm bells are blaring and questions are flying: How dangerous is this disease?

The disease itself is mild in most adults, with only about 20 percent of those who contract it showing any symptoms at all, mostly mild fever, headache, or rash. However, in newborns, cases of microcephaly — in which a baby is born with an unusually small head — are on the rise in Recife, the city in northeast Brazil at the center of the Zika outbreak, though health officials there haven’t yet definitively proven a causal relationship. Oddly, there have been few, if any, cases of Zika-related microcephaly so far across the rest of Latin America.

In the meantime, public health agencies aren’t wasting time issuing warnings: Brazil, Colombia, Ecuador, El Salvador, Jamaica, and Puerto Rico have already advised their citizens to avoid getting pregnant — a huge sacrifice for a disease that is still emerging, albeit rapidly. The U.S. Centers for Disease control has issued a travel warning for pregnant women thinking of visiting Zika-affected areas.