The United States reported nearly 1 million new coronavirus infections on Monday, the highest daily tally of any country in the world and nearly double the previous U.S. peak set a week ago as the spread of the highly contagious Omicron variant showed no signs of slowing.

The number of hospitalized COVID-19 patients has risen nearly 50% in the last week and now exceeds 100,000, according to data collected by Reuters, marking the first time that threshold has been reached in a year.

The latest surge, which forced waves of cancellations from commercial airlines flights to Broadway shows in recent weeks, was disrupting plans for public schools to welcome students back from winter vacation. In Chicago, union leaders were urging teachers in the nation’s third-largest school district to stay home as classrooms were reopening.

Nationally, the United States has seen a daily average of 486,000 new cases over the last week, a rate that has doubled in seven days and far outstrips that of any other country.

The 978,856 new infections documented on Monday including some cases tallied on Saturday and Sunday, when many states do not report.

The average number of U.S. COVID-19 deaths has remained fairly steady throughout December and into early January at about 1,300 a day, according to a Reuters tally, though deaths typically lag behind case numbers and hospitalizations.

Omicron appears to be far more easily transmitted than previous iterations of the virus. The new variant was estimated to account for 95.4% of the coronavirus cases identified in the United States as of Jan. 1, the U.S. Centers for Disease Control and Prevention (CDC) said on Tuesday.

The World Health Organization said on Tuesday that evidence thus far suggests Omicron is causing less severe illness. Nevertheless, public health officials have warned that the sheer volume of Omicron cases threatens to overwhelm hospitals, some of which are already struggling to handle a wave of COVID-19 patients, primarily among the unvaccinated.

Maryland Governor Larry Hogan declared a 30-day state of emergency on Tuesday and mobilized 1,000 National Guard members to pandemic response operations as COVID-19 hospitalizations in the state hit a record high of more than 3,000, up more than five-fold in the last seven weeks, Hogan said.

“The truth is that the next four to six weeks will be the most challenging time of the entire pandemic,” Hogan told reporters. He said projections show COVID hospitalizations could surpass 5,000, far higher than Maryland’s previous peak of 1,952 last year.

Delaware, Illinois, Ohio and Washington, D.C., also have reported record numbers of hospitalized COVID patients in recent days.

In Kentucky, where Tuesday’s total of 6,915 new cases was the highest daily figure since the start of the pandemic, Governor Andy Beshear urged residents to get vaccinated and wear masks.

“Omicron is causing a surge unlike anything we’ve seen and at this rate our hospitals will fill up,” he wrote on Twitter.

The unrelenting surge has prompted more than 3,200 schools to close their buildings this week, according to the website Burbio, which tracks school disruptions. Schools that have remained open are facing staff shortages and renewed concerns about virus spread. In Boston, where more than 54,000 students returned to class on Tuesday following the holiday break, Superintendent of Schools Brenda Cassellius told reporters there were 1,000 staff members out, including 461 teachers and 52 bus drivers.

“It does make for a difficult start to the day,” she said.

The governing body of the Chicago Teachers Union on Tuesday urged its members to stay out of the classroom and work remotely through July 18, or until the city reaches minimum health-safety thresholds set last year as a condition for in-person learning, whichever comes first. The union’s House of Delegates voted 88% in favor of the resolution, sending it to the 27,000 rank-and-file teachers and support staff to ratify by electronic ballot on Tuesday night. The union has called for more rigorous COVID-19 safety protocols, including school-based coronavirus testing and mandatory student vaccinations.

District chief executive officer Pedro Martinez said the school system would agree to further COVID-19 safety measures. But he said classes for Chicago’s 340,000 students would be canceled on Wednesday if teachers voted against reporting to work, with no remote instruction being made immediately available.

The union has cited data showing that vaccination rates remained especially low among minority students – with just 7% of Black youngsters and 13% of Latino children aged 5-11 fully inoculated. But school officials said hospitalization rates for children in Chicago are very low.

More than 325,000 COVID-19 cases among children were reported in the United States for the week ending Dec. 30, according to the American Academy of Pediatrics and the Children’s Hospital Association, a new high and almost double the count from the previous two weeks. The Biden administration was finalizing contracts for 500 million rapid coronavirus tests it plans to distribute for free to Americans, the White House said on Tuesday. The initiative is intended to help alleviate a testing crunch that has led to inadequate supplies and long lines in many places.