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

The omicron variant of the virus that causes COVID-19 has been found in Houston’s wastewater, the Houston Health Department announced Monday night. "The detection is the first indication the new variant is in Houston, although a case has not yet been confirmed in the city," the department said.

Wastewater samples collected between Nov. 29 and Nov. 30 showed omicron at eight of the city’s 39 wastewater treatment plants, and the genomic sequencing results confirming the variant were received Monday evening.

"The Houston Health Department and Houston Water continue to do an exceptional job tracking the impact of the virus in our community. While no specific case of the Omicron variant has been confirmed in an individual in the city of Houston, we should use this information as a reminder to get fully vaccinated, including a booster shot," Houston Mayor Sylvester Turner said in a statement. "Vaccines help protect us, our loved ones, friends, and colleagues in the work environment. As the holidays approach, I encourage everyone to remain vigilant about their health and safety."

The health department said it routinely tests the city’s wastewater for COVID-19, including variants, and recently started testing samples for omicron, as "people infected with COVID-19 shed the virus in their feces."

"The wastewater data helps to more quickly identify emerging outbreaks and hotspots needing interventions to help stop the spread of the virus," the health department added.

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