The head of the Centers for Disease Control and Prevention said Tuesday health officials are "actively looking for the omicron variant" in the United States but as of now, there is still no evidence that it exists within the U.S. Speaking at a White House COVID-19 briefing, Dr. Rochelle Walensky said the Delta variant "remains the predominant circulating strain" in the U.S., representing 99.9% of all sequencing samples. Dr. Anthony Fauci, the chief medical advisor to the White House, said as of Tuesday morning, the global case count hit 226 cases in 20 countries, which he said was rising "rapidly." Japan and France reported their first cases of the omicron variant Tuesday, while new findings indicate the mutant coronavirus was already in Europe close to a week before South Africa sounded the alarm. Much remains unknown about the new variant, including just how contagious it is, whether it makes people more seriously ill, and whether it can thwart the vaccine.