The highly contagious omicron variant is expected to infect more than half of Europe's population within the next two months, the World Health Organization's top official in the region warned Tuesday.

Over 7 million newly confirmed COVID-19 cases were reported across Europe in the first week of 2022, more than doubling over a two-week period. So far, 50 countries in the region have detected omicron infections, according to Dr. Hans Kluge, the WHO's regional director for Europe.

Kluge said omicron, which was first identified in southern Africa in November, "represents a new west-to-east tidal wave" and is "quickly becoming the dominant [variant] in western Europe and is now spreading in the Balkans."

"As of Jan. 10, 26 countries report that over 1% of their population is catching COVID-19 each week," Kluge told reporters during a press conference Tuesday. "At this rate, the Institute for Health Metrics and Evaluation forecasts that more than 50% of the population in the region will be infected in the next six to eight weeks."

More than 65,000 public school staff and students in Los Angeles have tested positive for COVID-19 as the nation's second-largest school district returns to classrooms on Tuesday.

The Los Angeles Unified School District is requiring all employees and students to get tested for COVID-19 before returning for the Spring semester. Staff headed back to campuses on Monday, while the first day of classes for students was pushed back to Tuesday.

As of Monday evening, 424,230 employees and students have been tested and 65,630 were positive for the virus. The student positivity rate stands at 16.6% and the employee positivity rate stands at 14.9%, according to data released by the Los Angeles Unified School District.

"Our positivity rate remains lower than the overall county positivity rate as a result of our heightened safety measures and the continued partnership of families and employees," the school district said in a statement Monday evening.

Since the start of the pandemic, Los Angeles County has reported a total of more than 2 million cases of COVID-19, with a positivity rate of 21.4%, according to data released Monday evening by the Los Angeles County Department of Public Health.

The U.S. Department of Defense announced a $442.1-million contract with Pfizer to produce 835,000 doses of Paxlovid, the first oral antiviral authorized to treat Covid-19. 

Pfizer CEO Albert Bourla said on Monday he expected distribution of the pill to rise "exponentially" in the coming months, with 6 million courses available by March. 

The Pentagon's announcement came less than a week after the White House announced it would double its purchase of Paxlovid from 10 million to 20 million treatment courses, with 10 million treatment courses ready by June.

The estimated completion for the Pentagon's contract was set for the end of March, officials said on Monday.

ABC News' Sasha Pezenik

The Chicago Teachers Union House of Delegates voted Monday to end the work stoppage, Chicago Mayor Lori Lightfoot said in a press conference.

Lightfoot said teachers will be back on Tuesday, and students will return on Wednesday.

"To the parents, we heard you. We will never, never, not have you at the table with us in the future. No one wins when our students aren't where they can learn their best," she said.

She explained that city officials and the CTU reached an agreement on when a school will go remote.

"Teachers are so important to who our young people become. That's not what this was about. We love our teachers and continue to support our teachers," Lightfoot added. "I will always be on the side of our children and their families."

The news of the work stoppage comes after Chicago Public Schools, the nation’s third-largest district, canceled classes for a fourth day Monday amid negotiations with the teachers’ union over remote learning and COVID-19 safety protocols.

"The Chicago Teachers Union House of Delegates has voted tonight to suspend the Union's remote work action while rank-and-file membership votes on the proposed agreement," CTU tweeted Monday night.