Severe flu season is sending many people to hospital emergency rooms across the country, including in the Chicago area.

The U.S. is seeing its highest level of respiratory illness in two decades; and the city of Chicago, Cook County, and the state of Illinois all are reporting "very high" flu levels.

Emergency department visits and hospitalizations for the flu are at their highest levels in three years in Chicago, and experts said it's not ending any time soon.

"This year, we're worried, because this amount of activity, although not unexpected, is really high," said Dr. Matthew Kippenhan, the medical director of the emergency department at Northwestern Memorial Hospital.

Kippenhan said his staff is seeing more people come to the hospital due to the flu, prompting concern.

"When we're seeing numbers and positivity testing this high, this early, we're really worried that it's going to be an even more severe season," he said.

Cook County officials said intensive care unit admissions for flu nearly doubled in the last week.

The Chicago Department of Public Health said emergency department visits and hospitalizations for flu are at their highest levels since 2022, most notable among children.

Doctors said it's in part because flu vaccination rates in Chicago are at about 23 percent, and 25 percent in the entire state. Both coverage rates are lagging behind previous seasons during the same time of year

"Obviously, we're concerned about it. We know that people that don't get their flu shot are more likely to get really sick and need hospitalization when they do get the flu," said Dr. Brian Borah, medical director for vaccine-preventable diseases surveillance at the Chicago Department of Public Health.

Borah said it's not too late to get the flu shot, calling it the best tool to protect against this season's strong flu strain.

"There is still some concern that this vaccine might not be a perfect match for this strain, but early data has shown that it is still very protective against hospitalizations and emergency department visits," he said.

On top of the flu shot, doctors said people should take steps like washing hands, wearing masks in crowded areas, and staying home if feeling sick to be safe.

Borah said the upward trend in flu cases and visits to the hospital is likely to continue in the near term.

"I think we still have some more time to see before we start to see these trends reverse," he said.

The city of Chicago and Cook County both offer vaccine clinics at multiple locations.