It’s difficult to understand how much of Europe’s wave can be attributed to relaxed precautions, waning immunity or intrinsic properties of BA.2, like its increased transmissibility.

But many of these countries have higher vaccination rates, especially higher booster rates in older adults, than the US.

“We’re playing with infectious disease fire right now,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.

The US has not reached the endemic phase yet, but even endemic viruses need careful management and steady funding, said Gregg Gonsalves, an epidemiologist at Yale School of Public Health. “We spend billions of dollars to keep things modestly in check. We’re not even doing that” with Covid.