Health authorities in the United States said the omicron variant of COVID-19 has become the dominant strain, just three weeks after the first case was reported in the country.

The U.S. Centers for Disease Control and Prevention(CDC) said on Monday that 73 percent of new infections across the country last week were of the omicron variant.

According to CDC data, omicron's share of infections expanded nearly six-fold in the past week, with over 650-thousand people estimated to have been infected with the variant during the same period.

The delta variant had been the dominant strain in the U.S. since late June, with more than 99-point-five percent of new cases being delta infections as recently as late November.