The Los Angeles County Department of Public Health said Thursday evening it has confirmed its first case of the omicron variant.

The county resident had recently traveled to South Africa, returning via London on Nov. 22, and the infection "is most likely travel-related," the department said.

The person is fully vaccinated and their symptoms are improving without medical care, health officials said. Several close contacts have all tested negative.

This is the second confirmed case of omicron in California, following identification Wednesday in a resident of San Francisco who had recently traveled to South Africa.

A new study from South Africa suggests that the new omicron variant might be more likely to lead to COVID-19 reinfection than prior variants, though more research is needed.

The study, which is not peer-reviewed, found that in November, there was an uptick in the rate of reinfections seen within three months of a primary infection, compared to prior surges driven by the delta and beta variants.

Researchers, who reviewed records of over 2.7 million people in South Africa with COVID-19 infections in 2020 and 2021, assumed many cases in November were caused by omicron, even though the first cases of the variant were not detected there until late November.

The vaccination status of individuals with suspected reinfections was unknown in the study, so it is unclear if they had immunity from prior infection or vaccination.

-ABC News' Dr. John Brownstein, Dr. Esra Demirel and Sony Salzman

Five cases of the new COVID-19 variant omicron have been detected in New York state, Gov. Kathy Hochul announced in a press conference Thursday evening.

Hochul emphasized that battling the delta variant is more of a challenge right now, adding that all five cases have been described as mild.

One case was located in Suffolk County, while three others were in New York City -- two in Queens and one in Brooklyn, Hochul said. A fifth suspected case has also been detected, the governor said, but did not provide details.

-ABC News' Will Gretsky

New York City's latest health mandate will require all nonpublic school employees to be vaccinated by Dec. 20, affecting 56,000 employees of 930 yeshivas, Catholic schools and other private schools.

-ABC News' Aaron Katersky

At least 10 people have tested positive for COVID-19 on a Cruise Norwegian ship disembarking in New Orleans this weekend, according to the Louisiana Department of Health.

Those infected include both passengers and crew members, officials said.

The Norwegian Breakaway departed from New Orleans on Nov. 28 and stopped in Belize, Honduras and Mexico on its voyage. There are more than 3,200 individuals on board, the health department said.

The company required on-site testing in addition to proof of vaccination before boarding the vessel, according to the Port of New Orleans.

The health department said the cruise line has been adhering to appropriate quarantine and isolation protocols. In addition, everyone aboard the ship will be tested for COVID prior to disembarking.

Those who test positive for COVID-19 on the ship will either travel by personal vehicle directly to their private residence or self-isolate according to current Centers fo Disease Control and Prevention guidelines in accommodations provided by Norwegian Cruise Lines.

"The health and safety of our guests, crew and the communities we visit is our highest priority, and we will continue to take all appropriate actions to ensure their wellbeing and protect public health," a Norwegian Cruise Lines spokesperson told ABC News.

"We have identified a handful of COVID-19 cases among guests and crew onboard Norwegian Breakaway, which is scheduled to disembark in New Orleans, LA on December 5. All of the identified cases onboard are asymptomatic. In addition to requiring that 100% of guests and crew are fully vaccinated, per the Company's comprehensive health and safety protocols, we have implemented quarantine, isolation and contact tracing procedures for identified cases."

The spokesperson said the company is testing all individuals prior to disembarkation, and providing post-exposure and quarantine public health guidance by the CDC.

"Any guests who have tested positive for COVID-19 will travel by personal vehicle to their personal residence or self-isolate in accommodations provided by the Company according to CDC guidelines," the spokesperson said. "We take this matter extremely seriously and will continue to work closely with the CDC, the office of Governor John Bel Edwards, the Louisiana Department of Health as well as the city and port of New Orleans. At this time, there have been no changes to scheduled future sailings on Norwegian Breakaway. We will provide additional updates to impacted guests as appropriate."