Omicron updates: COVID outbreak reported on cruise ship docking in New Orleans

The individual who tested positive for the first case of the omicron variant detected in the U.S. had received a full dose of the Moderna COVID-19 vaccine but was not yet eligible for a booster dose, according to San Francisco Department of Public Health Director Dr. Grant Colfax.

The person developed symptoms upon returning from South Africa, got tested in San Francisco and has since recovered, Colfax told reporters during a briefing Wednesday. 

"They did the right thing and got tested and reported their travel history," he said.

Colfax said the case is "not a cause for us to panic," and that San Francisco "is prepared" for this.

The health department has no plans at this time to change its current COVID-19 health orders, Colfax said.

The first case of the omicron variant in the U.S. has been identified in California, the California and San Francisco Departments of Public Health said.

The CDC said the person traveled from South Africa on Nov. 22.

The individual tested positive on Nov. 29, Dr. Anthony Fauci said at a briefing Wednesday.

The individual, who was fully vaccinated, had mild symptoms that are improving, the CDC said.

"All close contacts have been contacted and have tested negative," the CDC said.

"We knew that it was just a matter of time before the first case of omicron would be detected in the United States," Fauci said.

Fauci cautioned not to read into the mild symptoms of this single case and said the person was fully vaccinated but not boosted.

COVID-19-related hospital admissions in the U.S. are up by 20% since the beginning of November, according to federal data. About one-quarter of the patients are between the ages of 18 and 49.

Nearly 58,000 Americans are in the hospital with COVID-19, including more than 1,300 children, according to federal data.

-ABC News' Arielle Mitropoulos

In South Africa, the National Institute for Communicable Diseases reported 8,561 new COVID-19 cases on Wednesday -- which is nearly double the 4,373 new cases reported on Tuesday.   

Seventy-two percent of the new cases were diagnosed in Gauteng province. South African President Cyril Ramaphosa said Sunday that the omicron variant was responsible for most of the infections found in Gauteng over the last two weeks and that the variant is now showing up in all other provinces.

-ABC News' Christine Theodorou