California is reinstating an indoor mask mandate from Dec. 15 to Jan. 15.

Half of the state is already under a mask mandate per local rules, according to California Health and Human Services Secretary Mark Ghaly.

California is also tightening restrictions on unvaccinated people at large events. At events with more than 1,000 people, anyone who isn’t vaccinated must show proof of a negative antigen test within 24 hours or a negative PCR test within 48 hours.

State officials also recommend that travelers get tested three to five days before arriving in California.

-ABC News' Matt Fuhrman

Last week, another 164,000 children in the United States tested positive for COVID-19, up by 24% from the week prior, according to a report released Monday by the American Academy of Pediatrics and the Children’s Hospital Association.

COVID-19 cases among U.S. children are "extremely high," the organizations wrote in the report.

Last week the Northeast saw its highest number of pediatric cases since the onset of the pandemic, with nearly 40,000 new cases.

So far, 21 million children ages 5 to 17 nationwide -- about 39.6% -- have received at least one dose of a COVID-19 vaccine.

Severe illness due to COVID-19 remains "uncommon" among children, the organizations wrote in the report. But they continue to warn that there is an urgent need to collect more data on the long-term consequences of the pandemic on kids, including the physical, emotional and mental health impacts.

-ABC News' Arielle Mitropoulos

A total of 50 million COVID-19 cases have now been confirmed in the U.S., according to data from Johns Hopkins University.

The U.S. has reported more cases than any other nation in the world. The U.S. currently represents nearly one-fifth of the globe's total 270.5 million cases.

-ABC News' Arielle Mitropoulos

In the weeks following Thanksgiving, the COVID-19 resurgence in the U.S. has escalated rapidly.

The U.S. is averaging more than 118,000 new cases each day -- up by about 41.8% in the last two weeks and up nearly 85% since late October, according to federal data.

Six states with some of the nation's highest vaccination rates are also among the states with the highest new case rates: New Hampshire, Vermont, Massachusetts, Maine, Rhode Island and New York. Experts say cases could be rising in the Northeast partially due to people heading inside in the cold weather.

Daily COVID-19-related hospital admissions increased by 14.4% in the last week and jumped by 48% in the last month, according to federal data.

Pediatric admissions are up by 23.8% in the last week.

-ABC News' Arielle Mitropoulos

With winter closing in and COVID-19 cases on the rise, hospitals across the United States are once again facing the pressures of caring for thousands of patients.

More than 67,000 people are currently hospitalized with COVID-19 nationwide, according to federal data.

Rebecca Long, lead nurse in a COVID-19 intensive care unit at Nebraska Medical Center in Omaha, told ABC News that she and her team "literally do not have any ICU beds" available.

"I don't want anyone else's family member or loved one to have to be in the position where we say, like, we can't help you because we don't have the resources," Long said. "As health care providers, all we want to do is help people and we can't because we physically can't."

Dr. Kyle McCarty, medical director of emergency services at both HSHS St. Mary's and HSHS St. Vincent hospitals in Green Bay, Wisconsin, told ABC News that health care workers are feeling burned out after "being asked to do more with less."

"We're exhausted by the knowledge that we are the duct tape that is preventing a complete collapse of the health care system," McCarty said. "There's a national shortage of hospital staff, which is making it difficult to take care of patients the way that we want it. There aren't enough inpatient beds for the patients that need to be admitted to the hospital."

"This is a call for reinforcements, not a warning to stay away, because we don't want this to be the new normal," he added. "If we can recruit more health care teammates, it doesn't have to be."

-ABC News' Arielle Mitropoulos