The number of people being infected with the coronavirus continued to break records in Pennsylvania and New Jersey as the country crawled toward the new year, with the two states combined logging more than 43,000 cases in one day, according to numbers reported Thursday for the previous day.

Hospitalizations of children were also rising in Philadelphia, mirroring a national increase. Children’s Hospital of Philadelphia has had 10 to 25 inpatients a day with COVID-19 this month, compared with five to 10 in November.

And Delaware’s hospitalization rate jumped to the third-highest in the nation, according to New York Times data analysis, though the state’s daily case and hospitalization totals remain lower than those of larger states.

Starting Monday, Delaware will be under a state-of-emergency declaration, which will allow the state to mobilize National Guard troops for medical care and move patients between facilities, Gov. John Carney said Thursday.

“There’s a really simple solution to this dilemma — if you’re not vaccinated, get vaccinated. If you are vaccinated, be careful and wear a mask when you’re indoors,” Carney said at a briefing.

» READ MORE: Philly is averaging record-high COVID-19 cases, but officials hope this wave will have fewer hospitalizations

Spreading in tandem with delta, the more transmissible omicron variant is powering a record-breaking case surge across the United States. It appears to be causing milder cases and relatively fewer hospitalizations; still, hospitals are struggling with an influx of patients.

Most of those becoming very sick or being hospitalized are unvaccinated, meaning their severe illnesses were preventable, doctors and public health experts have emphasized this week. Those who are vaccinated tend to get milder cases if infected.

Public health officials said people should avoid New Year’s Eve gatherings and take precautions to minimize risk — including wearing a mask, even at outdoor events — if they decide to socialize. The Philadelphia Public Health Department strongly recommends residents not gather with other households.

“The safest thing to do would be to stay home and celebrate with those who are directly in your household,” said Temple Health physician Delana Wardlaw of Twin Sister Docs.

Rising hospitalizations for kids

At CHOP, children recently hospitalized with COVID-19 — more than half of whom likely have the omicron variant, according to the hospital — have had less serious symptoms than doctors were seeing pre-omicron.

“We’re seeing a lot of kids hospitalized with positive COVID tests but not necessarily with classic COVID symptoms,” Ron Keren, the hospital’s chief medical officer, said this week.

The virus seems to be causing less pneumonia and low oxygen levels, but doctors are seeing more symptoms that typically appear with routine respiratory illnesses — croup, bronchiolitis, fever, and exacerbated asthma.

Still, some child patients are seriously ill. They tend to be immunocompromised, obese, and older kids, Keren said. CHOP did not know what percentage of its COVID-19 patients were vaccinated. Citywide, about a quarter of all children 5 to 11 have received at least one vaccine dose, though rates among Black and Latino children are lagging.

» READ MORE: U.S. children hospitalized with COVID-19 in near-record numbers

Regionally, child hospitalizations for COVID-19 are higher than ever, the CDC reported this week. In Pennsylvania, Delaware, Maryland, Virginia, West Virginia, and Washington, D.C., a daily average of 44 children 17 and younger were admitted to hospitals due to COVID infections from Dec. 21 to 27, a nearly 52% increase from the prior week.

The rates of serious illness and death among children with COVID-19 remain exceedingly low, but any surge in virus hospitalizations causes problems for people in need of treatment for other reasons.

“It becomes difficult to care for children who come in with something acute because everybody is so overloaded,” said Philadelphia Health Commissioner Cheryl Bettigole.

Advice for New Year’s

New Jersey’s average number of new daily cases had climbed past 17,000 by Thursday, giving the state the third-highest case rate in the country after Washington, D.C., and New York. Its hospitalization rate was also rising.

And Pennsylvania, whose case surge began earlier, had one of the highest average totals of people hospitalized at 5,000. The state logged more than 16,700 new infections Wednesday and had an average daily case rate approaching 12,000, both higher numbers than ever before.

It makes for a grim situation heading into 2022. People should not attend large gatherings on New Year’s Eve, top White House adviser Anthony Fauci said this week, advice other health officials and doctors endorsed.

» READ MORE: What are the symptoms of omicron? Here’s how they differ in vaccinated and unvaccinated patients.

With the state of the pandemic’s rapid change over the last several weeks, Americans have struggled anew to make risk calculations. For many, the surge coincided with long-standing plans for holidays that people thought would mark a return to normal.

“There are people that are trying to get back to normal life, and omicron has definitely caused a detour,” said Wardlaw, the physician. “People are still going to venture out ... [but] err on the side of caution and wear your mask.”

The Thursday afternoon performance of Stomp at the Kimmel Center was canceled because of breakthrough cases among the cast. A spokesperson said replacements would enable Thursday night’s show to go on.

Wardlaw, who plans to ring in the new year at home with her husband and two children and via Zoom with other family members, recommended those who do choose to socialize should only gather with vaccinated people and should avoid large indoor or outdoor events, she said.

It’s also a good idea to take a rapid test before gathering, but if you can’t find one and have had COVID-19 exposure or symptoms, stay home, she advised.

In addition, it’s best to celebrate outdoors, increase ventilation indoors, keep gatherings small, and wear a mask, public health experts say. For small family gatherings, people should still take extra precautions like masking and distancing if someone who’s high-risk is there, added Montgomery County’s medical director, Richard Lorraine.

“Since the positivity rate and transmission levels are so high right now, we are recommending caution with any large indoor gathering,” Lorraine said.

Fireworks shows are planned at the Cherry Street Pier and Rivers Casino, along with other New Year’s events in the city. People in crowded places — like a fireworks display or the Mummers Parade — should wear a mask even if outdoors, said Philadelphia health department spokesperson James Garrow. Experts recommend wearing an N95 or KN95 mask or wearing both a surgical and a cloth mask.

“Then, make a resolution to make sure that you get every vaccine that you’re eligible for in 2022,” Garrow said. “That’s the best way to make sure that next year’s New Year’s celebration can be something closer to what we used to do.”

Staff writers Rob Tornoe and Peter Dobrin contributed to this article.