California has reported the first U.S. case of the omicron variant

The first case of the omicron variant of COVID-19 has been identified in the U.S., health officials said on Wednesday. The case was detected in a person in California, according to the Centers for Disease Control and Prevention.

"The individual was a traveler who returned from South Africa on November 22," the CDC said in a news release. "The individual, who was fully vaccinated and had mild symptoms that are improving, is self-quarantining and has been since testing positive. All close contacts have been contacted and have tested negative."

The case was identified in San Francisco

The San Francisco health department and California's state health department confirmed the case. In a joint statement, the two agencies said the variant was found thanks to the state's testing and genome sequencing surveillance.

"We must remain vigilant against this variant, but it is not a cause for panic," they said.

The case involves a resident of San Francisco who had recently been in South Africa, California Gov. Gavin Newsom said in a briefing about the case. She began her travel back into the United States on Nov. 21 and landed in San Francisco on Nov. 22, he said.

The person experienced COVID-19 symptoms on Nov. 25 and got tested three days later, according to the governor. He added that once the positive result was returned on Nov. 29, the sample was sent to the University of California, San Francisco, where genetic sequencing confirmed the coronavirus to be the omicron variant.

The person has not been hospitalized, Newsom said, adding that they're expected to recover fully.

The infected person had received two doses of the Moderna COVID-19 vaccine, but had not reached the six-month mark after the second shot in order to receive a booster shot, said Dr. Grant Colfax, director of health for the city of San Francisco.

"This person did what we hope other people would do when they arrive on a flight into the U.S.," Dr. Anthony Fauci, the president's chief medical adviser, said in a White House briefing. "They got off, and as soon as they became symptomatic, they went and got tested and it was positive."

Fauci added that as far as he's aware, the CDC is not investigating any other potential omicron cases in the U.S.

Omicron cases have been found in countries from Europe to the Middle East since the worrying new strain was first reported in South Africa last week. The U.S. now joins that list, which has grown despite countries' attempts to use travel restrictions to keep the omicron variant outside their borders.

The omicron variant's many mutations led the World Health Organization to say it poses a "very high" risk to global health. While warning that the evidence remains preliminary, the WHO says omicron's mutations "may be associated with immune escape potential and higher transmissibility."

When asked Wednesday if Americans should change any of their habits because of the variant, Fauci replied no, saying the CDC's overall guidance for vaccines and wearing masks has not changed.

'This will end,' Fauci says of the COVID-19 pandemic

The omicron variant's large number of mutations, including 26 to 32 in the protein spike alone, have quickly sparked fears that this version of the coronavirus could make COVID-19 spread more easily, and could be more likely to reinfect people who have already had COVID-19. As a result, omicron has also thrown both financial markets and personal expectations for a loop.

Toward the end of his briefing, Fauci was asked what he sees as the "end game" for the pandemic. He reiterated that the public in the U.S. and elsewhere must get vaccinated and boosted, to give the virus less room to spread and mutate.

"There's no doubt that this will end, I promise you that, this will end," Fauci said.

News of the U.S. omicron case in California comes after both President Biden and Fauci said they believed it was inevitable for the variant to surface in the U.S. They urged Americans to get vaccinated or get a booster shot, and to be vigilant about wearing masks.

"This variant is a cause for concern — not a cause for panic," Biden said.

South African officials raised the alarm about the heavily mutated variant, B.1.1.529, on Nov. 24. Two days later, the WHO classified it as a variant of concern and dubbed it omicron.

One week after the alarm was raised, omicron has been identified in at least 23 countries, the World Health Organization said on Wednesday.

The CDC recently updated its guidance on booster shots

On Monday, CDC Director Rochelle Walensky issued an update on the public health agency's advice for who should get a COVID-19 vaccine booster.

"Everyone ages 18 and older should get a booster shot either when they are 6 months after their initial Pfizer or Moderna series or 2 months after their initial J&J vaccine," she said in an statement.

This statement replaces earlier guidance that said people ages 18 and older but younger than 50 may receive a booster and others in certain at-risk categories or 50 and older should get a booster.

Walensky said the emergence of the omicron variant "further emphasizes the importance of vaccination, boosters and prevention efforts needed to protect against COVID-19."

Researchers are working to learn more about how the omicron variant behaves, particularly whether it's more likely to cause serious illness than other strains.

"It is not yet clear whether Omicron is more transmissible" or if it causes more severe disease, the World Health Organization said on Sunday.

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