This post originally appeared in The Atlantic.

Okay, good news first: Mosquito season in the United States is basically over—even in warmer regions, like Florida and areas along the Gulf Coast. “The risk of mosquito transmission of viruses goes way down by the end of October,” says Peter Hotez, a pediatrician and the dean for the National School of Tropical Medicine at Baylor College.

By early November, he told me, West Nile Virus and dengue fever pretty much “disappear” for the winter. Does this mean everyone can stop worrying about the Zika virus, too?

Well, here’s where the bad news comes in.

Zika isn’t a threat that’s going away anytime soon, despite the fact that in most areas of the U.S., cold weather brings the risk of mosquito-borne illnesses like Zika down to nearly zero. (In the Southernmost regions of Florida and Texas, the risk of such viruses declines in the winter, but doesn’t go away entirely.) The thing is, scientists still don’t understand Zika well enough yet to predict with certainty what’s going to happen in the months to come. It still seems like the outlook for Zika becomes more alarming with each new discovery. As my colleague Julie Beck wrote in September, we’ve learned a lot about the virus this year:

“Zika was determined to definitively cause the birth defect microcephaly and the neurological disorder Guillain-Barré. Scientists learned the mosquito-borne virus can also be spread sexually… by women as well as men, and that it can survive in semen for weeks or possibly months.”

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