The White House stated Wednesday that a resident of California who had been vaccinated against COVID-19 had become the first individual in the United States to be diagnosed with the omicron variant, as scientists continue to investigate the threats posed by the new virus strain.

According to Dr. Anthony Fauci, the individual was a traveler who returned from South Africa on November 22 and tested positive on November 29. The person had been vaccinated but had not had a booster dose, according to Fauci, and was having "moderate symptoms."

Late last month, the Biden administration took steps to restrict travel from Southern Africa, where the strain was initially discovered. Case clusters have also been discovered in around a half-dozen other countries.

"We thought it was only a matter of time before we saw the first case of omicron in the United States," Fauci added.

Officials stated that they had reached out to everyone who had had close contact with the individual and confirmed that they all tested negative.

The CDC is taking efforts to tighten US testing standards for international travelers, including demanding a test for all international travelers within a day of boarding a flight to the US, regardless of vaccination status. It was also thinking about requiring post-arrival testing.

Officials said the measures would only "buy time" for the government to learn more about the new variety and take proper precautions, but that its arrival in the United States was unavoidable due to its transmissibility.

Much about the new strain is unclear, including if it is more contagious than earlier strains, whether it causes people to get more seriously ill, and whether it may evade vaccination. Scientists will know more about the omicron strain in two to four weeks, according to Fauci, the top infectious disease expert in the United States, when they grow and test lab samples of the virus.

The first case in the United States comes as President Joe Biden prepares to reveal his strategy for combating influenza this winter on Thursday. Biden has attempted to calm fears about the omicron variant, saying that it is "a reason for concern but not panic."

Biden and public health experts have stepped up their calls for more Americans to get vaccinated — and for those who have already been inoculated to obtain booster doses to provide maximum protection against the virus.