First Case of Omicron Variant Reported in USThe first confirmed U.S. case of someone infected with the omicron variant of the coronavirus has been discovered in the Western state of California, U.S. health officials said Wednesday. The person returned to the U.S. from a trip to South Africa on November 22 and tested positive on Monday, Dr. Anthony Fauci, the country's top infectious disease expert and President Joe Biden's chief medical adviser, told reporters at the White House. Fauci said the person had mild coronavirus symptoms, was self-quarantining and was improving. The person was fully vaccinated, Fauci said, but had yet to get a booster shot. He said people who had been in contact with the infected traveler had tested negative for the coronavirus. The omicron case adds the U.S. to the growing list of at least 24 countries where the variant has been discovered. Fauci said researchers might know more in the next two weeks about the transmissibility of the variant and the degree to which existing vaccines protect people against it. Fauci and other health experts continued to urge the 60 million unvaccinated people in the U.S. to either get inoculated or get a booster shot if they have been vaccinated. "If you're eligible to get boosted, get boosted," he said. Fauci said that as people gather for holiday parties and family events in December, they can safely get together without wearing face masks if they know that others are vaccinated. But if they do not know that, he recommended wearing face masks to protect themselves and others. Jeffrey Zients, the White House COVID-19 response coordinator, said in a statement that Biden's medical team continued to believe that existing vaccines "will provide some level of protection against severe illness" from the omicron variant, and even more in people who received a booster shot. "This new variant is cause for continued vigilance, not panic," Zients said. The omicron discovery in the U.S. occurs as the Biden administration is reportedly preparing to impose stricter testing requirements for all international travelers entering the country, as part of an effort to curb the spread of the newly detected variant. News outlets say the administration will also require everyone entering the U.S. to undergo a COVID-19 test a day before their departure, regardless of their vaccination status. Officials are also discussing whether to require all travelers to self-quarantine for seven days after their arrival and to get retested within three to five days after entering the U.S. The proposed rules would also apply to U.S. citizens returning from overseas travel. Biden is expected to unveil the administration's new strategy in a speech Thursday. The U.S. joins a growing list of nations that have imposed some form of travel restrictions or outright bans on foreign travelers since the omicron variant was first identified November 24 by scientists in South Africa, according to the World Health Organization. Japan said Wednesday that it would ask all international air carriers to suspend new reservations for all flights into the country until the end of December in response to the growing outbreak of the omicron variant. The move by the Ministry of Land, Infrastructure, Transport and Tourism comes as Tokyo confirmed its second case of the new variant. Japan is also banning reentry of all foreign nationals with Japanese residency if they are traveling from South Africa or nine other southern African nations beginning Thursday. Along with the U.S., Saudi Arabia and Nigeria also reported their first cases of the omicron variant. The state-run Saudi Press Agency reported Wednesday that a Saudi citizen tested positive after traveling from a country in north Africa, while Nigerian authorities say its first cases of omicron were detected in samples collected back in October from two travelers who had arrived from South Africa. Meanwhile, the World Health Organization is recommending that people who are not fully vaccinated and who have underlying conditions, such as diabetes, that put them at increased risk of becoming severely ill or dying if they contract COVID-19 should postpone traveling to areas with high rates of community transmission. The WHO also declared that blanket travel bans imposed by countries will not prevent the global spread of the new variant but will instead "place a heavy burden on lives and livelihoods."