Members of Congress have been urged to work remotely as much as possible, as COVID cases are spiking across the country and within the halls of the Capitol, including many breakthrough cases among those vaccinated.

Brian P. Monahan, attending physician and top doctor for Congress, sent a letter to Congress members stating that due to "an unprecedented number of cases in the Capitol community affecting hundreds of individuals," the lawmakers should move to a "maximal telework posture," according to the letter obtained by the Associated Press.

While the House was not scheduled to hold session until next week, the Senate returned Monday for a session that lasted about 17 minutes before a vote scheduled for later in the day was postponed because of the amount of snow that was coming down in Washington, D.C.

Monahan cited the seven-day average rate of infection at the testing center in the Capitol, which has risen from 1 percent to over 13 percent, and as of Dec. 15, Monahan said about 61 percent of the cases have been identified as the Omicron variant, with 38 percent still the Delta variant.

In the letter, Monahan referred to mask wearing as "a critical necessity unless the individual is alone in a closed office space or eating or drinking in a food service area."

Capitol, Congress, COVID, Coronavirus, Omicron, Delta
The top doctor for Congress sent a letter to lawmakers Monday urging remote work to be conducted as much as possible as Omicron COVID cases spike nationwide, including within the U.S. Capitol, which is shown above.Robert Alexander/Getty Images

While providing no figure, Monahan said "most" cases at the Capitol are breakthroughs. Of those testing positive, 35% are asymptomatic, he said.

Monahan's letter came as the worldwide spread of the Omicron variant has prompted a deluge of COVID-19 cases, now averaging 400,000 reported new infections in the U.S. daily. The growing caseloads have caused cascading absentee rates at workplaces around the country including among schools, health care providers, airlines, police and fire departments and other essential workers, sparking concerns that disrupted services will only worsen in the near future.

"The daily case rates will increase even more substantially in the coming weeks," Monahan warned.

Spokespersons for Senate Majority Leader Chuck Schumer, D-N.Y., and House Speaker Nancy Pelosi, D-Calif., did not immediately have information on whether Monahan's letter might prompt any changes in Congress' operations. Regular lunches that Senate Democrats have together were expected to be virtual only for at least this week, said two people familiar with the emerging plans who spoke only on condition of anonymity.

Monahan urged congressional offices and agencies — which employ thousands of food service, custodial and other workers who serve Congress — to reduce in-person activities "to the maximum extent possible" by using electronic communications instead.

Currently, the House requires lawmakers and aides to wear masks in the House chamber except when they've been recognized to speak and in most other settings in the Capitol and House office buildings. The Senate encourages mask wearing but doesn't require it.

Monahan said people should wear properly fitted, medical grade KN95 masks or better. Blue surgical masks and cloth masks "must be replaced," he said.

Republican lawmakers and aides from both chambers are markedly less likely than Democrats to wear masks around the Capitol, with some rejecting widespread scientific acceptance that proper mask wearing can reduce the risk of spreading COVID-19 infections. Lawmakers can be fined up to $2,500 each time they don't wear a mask on the House floor, under a resolution the chamber approved last year, and several have been penalized.

Monahan said breakthrough cases have not led to any deaths or hospitalizations among vaccinated lawmakers or congressional staff.

But he said that while people who've received two vaccinations and a booster generally suffer mild symptoms, even those can lead to six to 12 months of "long COVID." That could include serious cardiovascular, neurological and cognitive problems, he said.

A "reasonable estimate" is that 6 percent to 10 percent of cases could end up that way, he added.

The Associated Press contributed to this report.