Flu cases are on the rise once again in the United States after reaching an all-time low last year.

The total number of cases could reach pre-pandemic levels, health experts say, potentially causing additional strain on the nation’s hospitals as they fight back a wave of Covid-19 cases fueled by the extremely contagious omicron variant.

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“I think it’s quite possible that we could have what we would term ‘a normal flu season,’” said Lynnette Brammer, an epidemiologist who leads the Centers for Disease Control and Prevention’s domestic influenza surveillance team. “In a lot of cases, we’re already seeing more flu activity than we saw with all of last year.”

The CDC has reported more than 4,500 flu cases from clinical laboratories nationwide for the week ending Dec. 18, up from about 2,500 cases two weeks earlier. Flu experts say they expect cases to continue to increase over the next several weeks.

The eastern and central parts of the country are seeing the most influenza activity, while the western parts are still reporting lower levels of the virus, but that could change in a few weeks, Brammer said.

“The flu is unpredictable,” she said. “Some years, it’ll start in the South and move up. Sometimes, it’ll start on both coasts and move in. It does not have a consistent pattern to it.”

CDC data shows most cases are of the H3N2 lineage — a strain that experts say is particularly troublesome, as it tends to mutate faster than other variants of influenza and can cause more hospitalizations. 

Visits to doctor’s offices, urgent care clinics and hospital emergency rooms for influenza-like illness— which the CDC describes as people who report fever, cough and a sore throat — surpassed the national baseline for the second week in a row, according to agency data. Hospitalizations for influenza also started to increase over the last two weeks.

Two children died from the flu this month. In a typical year, the U.S. has anywhere between 150 to 200 pediatric deaths from the flu, but the two deaths in December were the first pediatric deaths due to the disease in over a year.

Flu experts had previously said they were concerned that the country could be at risk for a severe flu season this year after seasonal flu cases reached record lows last year. In addition, some research suggests vaccine effectiveness against the current dominant flu strain may be reduced this season; however, the shots are still likely to offer protection against serious illness and death, experts say.

Flu cases were “substantially lower” during the 2020-21 influenza season because people were protecting themselves, including by working remotely, wearing masks and practicing social distancing, said Dr. Mark Roberts, director of the Public Health Dynamics Laboratory at the University of Pittsburgh.

He said he’s concerned that regions of the country that currently don’t have mitigation measures for Covid will see a large increase in flu cases in the coming weeks.

“What I think is worrisome now is that there are many states where they’re not doing much to try to prevent Covid,” Roberts said. “They’re getting rid of mask mandates, they’re letting people come indoors, and there’s quite a bit of variability in how states are handling the situation.”

Nancy Foster, vice president of quality and patient safety policy at the American Hospital Association, said a nationwide flu outbreak could add additional stress on the doctors, nurses, respiratory therapists and other health care workers who are already battling a surge in Covid cases.

The dual presence of Covid and flu could leave health care workers even more susceptible to illness, leading some to have to call out of work, she said.

The viruses wouldn’t just have an impact on doctors and nurses who care for patients.

“If our housekeeping staff are out, we can’t turn around a room quickly or make sure that everything is as clean as it needs to be so that a new patient can be admitted,” she said. “If the food service workers are out, we can’t get meals to people.”

The CDC’s Brammer urged the public to take “common sense” precautions, including getting vaccinated, covering one’s mouth when coughing or sneezing, washing hands, and staying home if they are sick.

“And if you do get sick with the flu, particularly if you have severe illness or have high-risk chronic conditions that make you at risk for having severe influenza, talk to your doctor quickly because there are antiviral drugs that can keep you from getting severely ill,” she said.

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