NEW YORK (AP) — A second wave of flu is hitting the U.S., turning this into one of the nastiest seasons for children in a decade.

The number of child deaths and the hospitalization rate for youngsters are the highest seen at this point in any season since the severe flu outbreak of 2009-10, health officials said Friday. And the wave is expected to keep going for weeks.

Experts say it is potentially a bad time for an extended flu season, given concerns about the new coronavirus out of China, which can cause symptoms that can be difficult to distinguish from flu without testing.

If coronavirus were to begin spreading in the U.S., there could be confusion about whether people are getting sick with it or the flu, said Dr. William Schaffner, an infectious-diseases expert at Vanderbilt University.

This flu season got off to its earliest start in 15 years, with surges of flu-like illnesses seen in parts of the South as early as October. Most cases were caused by a type of flu that usually causes substantial infections only in the spring, at the tail end of the flu season.

That wave peaked in late December and dropped steadily for weeks afterward.

But a second surge began in late January. Last week saw another rise in the percentage of doctor’s office visits that were due to flu-like illness, according to the U.S. Center for Disease Control and Prevention.

“We have not yet peaked for influenza. We are still on our way up,î Dr. David Weber, a University of North Carolina infectious-diseases specialist, said of the patient traffic in Chapel Hill.

Overall, the CDC estimated that 26 million Americans have gotten sick with flu this past fall and winter, with about 250,000 flu-related hospitalizations and around 14,000 deaths.

The viruses behind both waves can be hard on children and young adults. But they aren’t considered as dangerous to retirement-age people — good news, since most flu deaths and hospitalizations each winter occur in the elderly.