Flu is surging nationwide. Hospitalizations nearly doubled in a single week.

Dr. Jennifer Goebel, an attending physician at South Shore University Hospital in Northwell in New York, said the hospital began seeing a spike in flu cases around Thanksgiving, and maybe even a little earlier.

“I don’t remember seeing flu cases this early or in such large numbers,” Goebel said. “Seems worse. Just huge volume.”

Dr. Donald Yealy, chief medical officer of the UPMC health system, which has hospitals in Pennsylvania, Maryland and New York, said he has seen a “dramatic increase” in the number of people being admitted with acute respiratory infections over the past two weeks.

“Most of them are people with suspected influenza,” Yealy said. “And of the ones we have adequate testing for, it is disproportionately influenza A.”

Who is hit hardest this flu season?

Doctors say infants and young children under 4 years of age have been hit the hardest.

But as cases rise, Dr. Lauren Suney, medical director of the emergency department at Duke University Hospital in North Carolina, said school-aged children and young adults are also getting sick from the flu.

Older people and people with chronic illnesses are more likely to need hospitalization, Sivney added. Beds are also tight because Covid and RSV cases overlap with those of flu patients, she said.

“We have built-in plans for these surges and we prioritize the sickest patients first,” Sivney said.

Yealy said the flu affects all age groups, although the vast majority of people who require hospitalization or extended care are not vaccinated.

They are also seeing a slight increase in Covid, norovirus and RSV cases, but the majority of cases are due to influenza.

“We are in the midst of a winter virus season,” he said.

South Shore University Hospital's Goebel also said they're seeing cases across all age groups, adding, “We're really just seeing it across the board.”

Is the new variant a “super flu”?

The dominant strain now is influenza A, a fast-spreading mutated H3N2 strain called “subclade K.” It is generally believed that H3N2 cause more severe illnesswhich may explain the sudden rise in hospitalizations.

The mutated strain, dubbed “super flu,” emerged over the summer and includes changes to a key surface protein that may make it difficult for the immune system to recognize the virus. It is also blamed for causing severe and early flu seasons in the UK and Japan.

Dr. Wenqing Zhang, who heads the World Health Organization's global respiratory threats unit, wrote in a recent blog post that current data does not suggest an increase in disease severity from the new strain.

“Although the genetic shift leads to a noticeable evolution of the virus,” Zhang wrote.

What are the symptoms of the flu variant?

Dr. Molly Fleece, an assistant professor of infectious diseases at the University of Alabama at Birmingham, said symptoms were essentially unchanged from previous flu seasons.

“The onset of symptoms is acute,” she said. “People experience fever, shaking, chills, cough, shortness of breath and muscle pain.”

Symptoms can be more severe, especially if the person is not vaccinated, Fleece said. Older adults and people with underlying health conditions also report more serious complications, including pneumonia, muscle breakdown and seizures.

Goebel said patients also report headaches or fatigue, and in some cases nausea, vomiting and diarrhea.

“If patients experience shortness of breath, if patients have a high fever despite taking Tylenol and Motrin around the clock, or have any problems at all, we encourage them to seek medical attention,” she said.

Should I get a flu shot?

Doctors say it's not too late to get vaccinated.

This year's flu shot contains an H3N2 component, although it doesn't exactly match the mutated strain, Fleece said. “This is because the subclade mutated and spread after the vaccines had already been selected for that year.”

But that doesn't mean the vaccine isn't effective, she added.

“This may mean more people will be susceptible to flu illness… but we know from historical data that the vaccine is still very effective in preventing severe illness, hospitalization and death.”

Yealy said the vaccine will “essentially arm your body with the appropriate response before you get infected.”

“This year's seasonal vaccine may help provide protection,” he said.

Other winter viruses circulating

Flu is dominant now, but Covid cases are slowly rising across the country, according to data from WastewaterScan, an academic program at Stanford University in partnership with Emory University. Covid levels are high in the South, Northeast and Midwest.

Norovirus infections, which spiked in late November, are still high and rising.

Respiratory syncytial infection (RSV) is on the rise, especially in the South, WastewaterScan data shows.

Doctors say it is possible to contract more than one viral infection at the same time, a situation that can make the disease worse.

“Having one virus doesn’t actually prevent another,” Yealy said. “The more serious problem is the presence of one of the respiratory viruses and the deterioration of the second condition.”