Flu is taking off in the U.S., with 40 states reporting high or very high levels of flu-like illness last week.

Emergency room visits with influenza are now "very high" nationwide, the Centers for Disease Control and Prevention said Friday, in this week's update on the winter respiratory virus season.

It’s been increasing at a pretty steady pace now for the past several weeks. So yeah, we are certainly in flu season now.” ...

So far this season, the CDC estimates, there have been at least 5.3 million flu illnesses, 63,000 hospitalizations, and 2,700 deaths — including at least 11 children. It’s not clear if this ...