Omicron updates: COVID-19 cases could double in New York City

French Prime Minister Jean Castex announced that the country's night clubs will be closed for four weeks starting Friday, amid rising cases in the country.

"We are doing this because the virus is spreading amongst young people, even those who are vaccinated, because it is extremely difficult to keep a mask on at these venues," Castex said at a news conference Monday.

The decision came after the French Health Defense Council held a meeting to decide on what new health measures have to be taken to stop the spread of the virus in France.

Castex also announced that primary school students would have to wear face masks at recess and between classes -- not only inside the classroom -- starting Thursday.

France will not follow other European Union countries, like Germany and Italy, that are imposing restrictions on unvaccinated residents, the prime minister said.

-ABC News' Christine Theodorou

Los Angeles health officials announced Monday a second case of the omicron variant was detected in the county.

The patient is a student at the University of Southern California, who was returning from a trip from the East Coast, according to the Los Angeles County Department of Public Health.

The student likely acquired the infection outside of LA county, health officials said in a statement.

"The individual is fully vaccinated, had mild symptoms, and is self-isolating," the health department said in a statement.

Officials at USC said the student "did not attend classes or organized activities on campus during their infectious period."

-ABC News' Bonnie McClean and Jen Watts

Another 133,000 children tested positive for COVID-19 last week, according to a new report from the American Academy of Pediatrics and the Children’s Hospital Association. Hospital admissions among children have also increased by 20% over the last week, according to federal data.

The Northeast is currently seeing its highest number of child cases since the beginning of pandemic, though the Midwest continues to see the highest number of pediatric cases. 

Twenty million children ages 5 to 17 have received at least one vaccine dose, accounting for about 38.3% of that population.

Severe illness due to COVID-19 remains "uncommon" among children, the two organizations wrote in the report. However, AAP and CHA continue to warn that there is an urgent need to collect more data on the long-term consequences of the pandemic on children, "including ways the virus may harm the long-term physical health of infected children, as well as its emotional and mental health effects."

-ABC News' Arielle Mitropoulos

Mississippi said it's confirmed its first case of the omicron variant, detected in a fully vaccinated person who recently traveled to New York, the state's Department of Health said.

The person's symptoms were not released but the health department said the individual was not hospitalized. 

Mississippi is seeing "a minimal increase in the number of COVID patients in the hospital and a minimal increase of COVID patients in the ICU and on vents," the Department of Health added.

-ABC News' Michelle Stoddart