(Follow link for 4 minute NPR news podcast.)

The flu virtually disappeared for two years as the pandemic raged. But influenza appears poised to stage a comeback this year in the U.S., threatening to cause a long-feared "twindemic."

While the flu and the coronavirus are both notoriously unpredictable, there's a good chance COVID cases will surge again this winter, and troubling signs that the flu could return too.

"This could very well be the year in which we see a twindemic," says Dr. William Schaffner, an infectious disease professor at Vanderbilt University. "That is, we have a surge in COVID and simultaneously an increase in influenza. We could have them both affecting our population at the same time."

The strongest indication that the flu could hit the U.S. this winter is what happened during the Southern Hemisphere's winter. Flu returned to some countries, such as Australia, where the respiratory infection started ramping up months earlier than normal, and caused one of the worst flu seasons in recent years.

What happens in the Southern Hemisphere's winter often foreshadows what's going to happen north of the equator. ...