Congress' top doctor urged lawmakers on Monday to move to a "maximal telework posture," citing surging numbers of COVID-19 cases at the Capitol that he said are mostly breakthrough infections of people already vaccinated. 

The seven-day average rate of infection at the Capitol's testing center has risen from less than 1% to more than 13%, Brian P. Monahan, the attending physician, wrote in a letter to congressional leaders obtained by The Associated Press. 

Monahan said there has been "an unprecedented number of cases in the Capitol community affecting hundreds of individuals." In what he said was limited sampling as of Dec. 15, about 61% of the cases were the new, highly contagious omicron variant while 38% were the delta variant. 

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Clouds hang over the U.S. Capitol on Dec. 29, 2021, in Washington. (Anna Moneymaker/Getty Images)

While providing no figure, he said "most" of the cases are breakthroughs. 

While such cases have not led to any deaths or hospitalizations among vaccinated lawmakers or congressional staff, he said even mild infections can lead to six to 12 months of "long COVID." A "reasonable estimate" is that 6% to 10% of cases could end up that way, he added. 

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Visitors from France enjoy the scenery as a winter storm delivers heavy snow to the Capitol in Washington, Monday, Jan. 3, 2022. (AP Photo/J. Scott Applewhite)

Monahan urged congressional offices to "reduce in-person meetings and in-office activities to the maximum extent possible." 

And he said wearing a properly fitted, medical grade KN95 or better mask is "a critical necessity unless the individual is alone in a closed office space or eating or drinking in a food service area."