The Omicron variant pushed Covid-19 daily cases in the U.S. to the highest level in nearly a year, leading to the cancellation of more than 2,000 flights over the holiday weekend and signaling the different kind of threat that the surging new strain poses to the economy and everyday life.

Evidence so far suggests the Omicron variant generally leads to less-severe disease than earlier strains of the virus. But the travel cancellations show how even a milder but rapidly spreading version of Covid-19 can disrupt business activity and people’s plans.