The first documented COVID-19 case caused by the Omicron variant of the coronavirus has been detected in a fully vaccinated patient who flew to South Africa and returned to the U.S.

Health officials said the infected individual had shown moderate COVID-19 symptoms. The person reportedly arrived in the U.S. on Nov. 22 and then tested positive seven days later.

Dr. Anthony Fauci, the top U.S. infectious disease expert, who briefed reporters at the White House, said the patient was completely vaccinated but had not had a booster dose. He added that the patient is now in quarantine in California, and so far, all of the person’s close contacts have tested negative.

Not a lot is still known about the new variety, which altered in ways that health experts believe may boost its ability to spread and elude some vaccination protections.  Omicron is found in more than a dozen nations, including several in Europe and Canada, Australia, Japan, Hong Kong, and Israel. In South Africa, Omicron currently makes up three-quarters of all COVID-19 samples.

Omicron community transmission has yet to be identified in the United States. COVID-190 transmission is high over much of the country, although new cases have been relatively stable over the previous two weeks.

Fauci claims that it might take two weeks or longer to learn how quickly the variation spreads from person to person, how severe the symptoms are, and whether it can get through the present vaccination safeguards.

As a precaution, nearly all visitors who have visited one of eight southern African nations have been forbidden from entering the United States. The CDC ordered airlines to release the names and other information of passengers who had visited certain countries on Tuesday.

The Biden administration has advised fully-vaccinated Americans to obtain booster injections also as a precaution. According to the United States Department of Health and Human Services, 60% of Americans are completely immunized, with around a fifth having received booster shots.