Omicron sub-variants that have been circulating since December—called BA.1.1 and BA.1.1.529—now makeup around 57.3% and 7.9%, respectively, of circulating variants.
Covid-19 infections in the US have receded sharply since hitting record levels in January. As of 20 March, the seven-day moving average of the infections was 27,786, down 17.6% from a week earlier.
The CDC estimates that BA.2 made up 22.3% of circulating variants in the country for the week ending 12 March, revised down from 23.1%, according to a CDC model that estimates proportions of circulating variants.
Most of the US is considered to have low transmission, under new CDC guidelines introduced last month, which emphasized hospitalization rates and advised most Americans they no longer needed to wear masks.