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

The U.S. Centers for Disease Control and Prevention updated its guidance on COVID-19 testing and is advising people, even those who are vaccinated, to get a test before they head to an indoor gathering.

The agency said a rapid test ahead of a gathering is important if the gathering includes unvaccinated children and older people who are more vulnerable to COVID-19.

“Even if you don’t have symptoms and have not been exposed to an individual with COVID-19, using a self-test before gathering indoors with others can give you information about the risk of spreading the virus that causes COVID-19," the CDC said in its guidance.

-ABC News' Anne Flaherty

Harris County, Texas, Judge Linda Hidalgo tweeted Monday night that the area recorded its first case of the omicron COVID-19 variant.

The judge shared few details about the case but said the patient was "a woman in her 40s from [north west] Harris County with no recent travel history."

-ABC News' Scottye Kennedy

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