One month ago, the CDC published the results of more than 20 pandemic forecasting models. Most projected that COVID-19 cases would continue to grow through February, or at least plateau. Instead, COVID-19 is in retreat in America. New daily cases have plunged, and hospitalizations are down almost 50 percent in the past month. This is not an artifact of infrequent testing, since the share of regional daily tests that are coming back positive has declined even more than the number of cases. Some pandemic statistics are foggy, but the current decline of COVID-19 is crystal clear.

What’s behind the change? Americans’ good behavior in the past month has tag-teamed with (mostly) warming weather across the Northern Hemisphere to slow the pandemic’s growth; at the same time, partial immunity and vaccines have reduced the number of viable bodies that would allow the coronavirus to thrive. But the full story is a bit more complex.