While BA.5 is still the nation's dominant strain, its prevalence has fallen over the past two weeks, according to the CDC's latest estimates.
The subvariant now accounts for 84.8 percent of all U.S. COVID-19 cases — down slightly from 86 percent a week prior, according to estimates for the week ending Sept. 17.
At the same time, the proportion of other omicron offshoots is rising. Two updates:
1. BA.4.6's prevalence hits double digits. The subvariant's prevalence has been ticking up since mid-June, when it accounted for less than 1 percent of U.S. cases. Now, BA.4.6 accounts for 10.3 percent of all U.S. cases, up from 9.4 percent the week prior.
Scientists are still trying to learn more about BA.4.6, which has a mutation that allows it to evade immunity, similar to other omicron subvariants. A study published Aug. 10 in the preprint server BioRxiv suggests BA.5 infection would likely not protect against reinfection from BA.4.6.
2. CDC is now tracking BA.2.75. Thirty-eight states and the District of Columbia have reported BA.2.75 cases as of Sept. 8, up from 20 states a month prior, according to a dashboard that uses data from GISAID, a global data-sharing platform for viruses.
As of last week, the CDC started tracking BA.2.75 separately from BA.2 due to its positive growth rate, the agency said in its COVID-19 data tracker weekly report published Sept.16. The subvariant accounted for 1.3 percent of all U.S. COVID-19 cases in the week ending Sept. 17, CDC data shows.
Scientists have closely monitored the variant this summer to assess its risk of competing against BA.5 or causing more severe disease. Emerging research suggests the variant may not pose a large threat to public health.