The seven-day positivity rate at the U.S. Capitol COVID-19 testing center has increased from 1% to 13%, according to a letter sent from the Office of the Attending Physician to congressional offices on Monday.

Most cases have been breakthroughs among people who are fully vaccinated and have not “led to hospitalizations, serious complications, or deaths, attesting to the value of coronavirus vaccinations," the letter reads.

The letter also states that about 61% of COVID-19 infections at the Capitol have been linked to the omicron variant, and 38% are linked to the delta variant.

The OAP advised congressional offices to telework as much as possible and that "blue surgical masks, cloth face masks and gaiter masks must be replaced by the more protective KN95 or N95 masks."

New York City Mayor Eric Adams insisted that schools will stay open for in-person leaning despite the rapidly rising number of COVID cases.

“We’re really excited about the opening of our schools,” he said during a speech outside Concourse Village Elementary School in the Bronx on Monday. “We want to be extremely clear: the safest place for our children is a school building.”

As part of a plan to curb rates of infection, 1.5 million rapid at-home test kits are being being distributed to schools.

Students and adults who exhibit symptoms or have been exposed to a positive case will be required to have two negative tests over the course of five days before they can return to classes.

On Sunday, Adams told ABC's "This Week" that parents should "fear not sending [kids] back" to school after the winter break.

Meanwhile, several other school districts across the country, including Atlanta, Cleveland, Newark and Milwaukee, have opted for virtual learning for at least the first week of the new semester.

More than 100,000 Americans are currently hospitalized with COVID-19, according to data from the U.S. Department of Health and Human Services.

A total of 103,329 people are receiving medical care, which is an increase of 130% from the number recorded two months ago.

Of those patients, more than 17% -- about 18,000 -- are in intensive care units.

The newly updated figure is just shy of the hospitalization peak seen during the summer wave fueled by the delta variant, when 104,000 Americans were hospitalized with COVID in early September.

-ABC News' Arielle Mitropoulos

The U.S. Food and Drug Administration authorized booster shots of Pfizer-BioNTech's COVID-19 vaccine in children between ages 12 and 15 on Monday.

Booster shots have been touted as a key tool in fighting the surge in COVID cases linked to the omicron variant, which has shown an ability to -- at least partially -- evade protection offered by two doses.

The FDA also shortened the wait period for adults and adolescents to receive boosters from six months down to five months.

In addition, the agency authorized COVID booster shots for children aged five to 11 who are immunocompromised.

The state of New York has told 40 hospitals they must turn away nonessential, nonurgent elective surgeries for the next two weeks in response to low bed capacity. Most of the hospitals are located in upstate New York.

The determination was made after the hospital locations were added to the list of "high risk regions" by the state department of health due to 90% of beds being occupied according to the seven-day average.

"We will use every available tool to help ensure that hospitals can manage the COVID-19 winter surge," acting State Health Commissioner Dr. Mary Bassett said in a statement Saturday. "I want to remind New Yorkers that getting vaccinated and boosted remain the best way to protect against serious illness and hospitalization from COVID-19. Vaccination also protects our hospital system. We cannot return to the early months of the pandemic when hospitals were overwhelmed."

All of the hospitals in three regions -- Mohawk Valley, Finger Lakes and Central New York -- are included in those 40 facilities.