The number of Americans hospitalized with Covid-19 has surpassed last winter’s peak, underscoring the severity of the threat the virus continues to pose as the extremely contagious Omicron variant tears through the United States.

As of Sunday, 142,388 people with the virus were hospitalized nationwide, according to data from the U.S. Department of Health and Human Services, surpassing the peak of 142,315 reported on Jan. 14 of last year. The seven-day average of daily hospitalizations was 132,086, an increase of 83 percent from two weeks ago.

The Omicron wave has overwhelmed hospitals and depleted staffs that were already worn out by the Delta variant. It has been driven in large part by people younger than 60. Among people older than 60, daily admissions are still lower than last winter.

The hospitalization totals also include people who test positive for the virus incidentally after being admitted for conditions unrelated to Covid-19; there is no national data showing how many people are in that category.

As cases soared over the past few weeks to an average of over 737,000 per day, far higher than last winter’s peak, public health officials have argued that caseloads were of limited significance because Omicron is less virulent than Delta and other variants, and that vaccines, and especially boosters, offered protection against severe illness.

But the surge’s sheer volume has overwhelmed hospitals across the country. And outside cities like New York, where Omicron hit early and has pushed hospitals to the brink, it is unlikely to have peaked.

Current hospitalizations are one of the most reliable measures of the severity of the pandemic over time, because they are not influenced by testing availability or by spikes in minor cases.

Dr. Anthony S. Fauci, the country’s top infectious diseases expert, told ABC News last week that it was “much more relevant to focus on the hospitalizations,” which lag behind cases.

About a quarter of U.S. hospitals are experiencing critical staffing shortages, according to the Department of Health and Human Services. Some states, like Oregon, have deployed the National Guard to help. Others, like Illinois and Massachusetts, are delaying elective surgeries — meaning surgeries that are scheduled, as opposed to an emergency, a category that can include procedures like a mastectomy for a cancer patient. In some cases, employees with asymptomatic or mildly symptomatic coronavirus infections have been working, potentially putting patients at risk.

After nearly two years, “even the most dedicated individuals are going to be tired and worn out, if not burned out and dealing with mental health issues as a consequence,” said Dr. Mahshid Abir, an emergency physician at the University of Michigan who is a researcher at the RAND Corporation.

Data in some of the first cities hit by Omicron also show deaths spiking sharply — not as fast as case rates, but fast enough to warn of more devastation to come.

Doctors, nurses and other medical personnel are also falling ill themselves, and while most are vaccinated and have not needed hospitalization, their illness still keeps them out of work. Now, hospitals overwhelmed by coronavirus patients are ill equipped to handle other emergencies like heart attacks, appendicitis and traumatic injuries.

“The demand is going up and the supply is going down, and that basically doesn’t paint a good picture for people and communities — not just for Covid, but for everything else,” Dr. Abir said.