The United States on Wednesday identified its first known COVID-19 case caused by the omicron variant, discovered in a fully vaccinated patient who had traveled to South Africa, as scientists continue to study the risks the new version could pose.
Public health officials said the infected person, who had mild and improving symptoms, returned to the United States from South Africa on Nov. 22 and tested positive seven days later.
That patient was fully vaccinated but had not had a booster shot, according to Dr. Anthony Fauci, the top U.S. infectious disease official, who briefed reporters at the White House.