Since omicron first appeared in the U.S. nearly a year ago, the variant has maintained dominance, splintering into an increasingly complicated patchwork of sublineages.
The original omicron variant was first detected in the U.S. in early December 2021, and by Dec. 18, it had grown to account for more than 70 percent of cases. In late June, the BA.5 sublineage emerged and quickly rose to dominance.
But now, BA.5 is receding as other omicron relatives take over, accounting for less than 30 percent of cases for the week ending Nov. 12, according to CDC variant proportion estimates.
In what appears to be a good sign, U.S. cases have remained relatively stable since October, despite new omicron relatives' growth, according to HHS data compiled by The New York Times. The nation's seven-day case average was 39,414 as of Nov. 15, though this is likely an undercount since it does not include at-home test results.
Due to a high level of variant diversity, experts say a potential uptick in COVID-19 cases this winter would likely be driven by several different lineages, rather than just one. Helix, a lab that helps the CDC track variants, said BQ.1, BQ.1.1 and BF.7 are on its watchlist because of their potential for immune escape.
Here is a breakdown of the five most prevalent omicron subvariants, listed in order of their estimated case proportions for the week ending Nov. 12:
BQ.1.1 — 24.1 percent prevalence
BQ.1 — 20.1 percent prevalence
Dubbed "escape variants" for their immune evasiveness, BQ.1 and its descendant BQ.1.1 started gaining traction in October. Together, the pair are now dominant, accounting for 44 percent of U.S. cases. Early studies have suggested BQ.1 can evade immunity from vaccines or past infection, though may not cause more severe illness. Disease experts have described the pair as "the most evasive yet" because of their ability to completely resist monoclonal antibody drugs. Experts have remained optimistic that the bivalent omicron boosters will offer protection against the pair since they're descendents of BA.5, which the updated shots were designed to target.
BF.7 — 7.8 percent
The CDC started tracking BF.7 in late September. The subvariant's prevalence more than doubled last month, jumping from 3 percent in the week ending Oct. 1 to 7.5 percent in the week ending Oct. 29. However, this growth rate appears to have slowed, as the subvariant's prevalence has hovered around 8 percent for the past three weeks, according to CDC data. BF.7 has one additional genetic mutation in the spike protein compared to BA.5, its parental strain.
"Data indicates that this specific genetic change could reduce the efficacy of Evusheld," CDC spokesperson Jasmine Reed told CBS News. AstraZeneca's Evusheld is one of few monoclonal antibody drugs that still works against BA.4 and BA.5. Ms. Reed said there are no signs that BF.7 would impede COVID-19 vaccines or diagnostic tests.
BA.4.6 — 5.5 percent
BA.4.6 — a sublineage of BA.4 — has a mutation that allows it to evade immunity, much like other omicron subvariants. A study published Aug. 10 in the preprint server bioRxiv suggests a past BA.5 infection would likely not protect against reinfection from BA.4.6. The subvariant's prevalence steadily rose in the second half of summer before peaking at 11.1 percent in the week ending Sept. 24, CDC data shows.
BN.1 — 4.3 percent
The CDC started tracking BN.1 in its latest variant proportion update published Nov. 11. The strain was first identified in September and descends from the BA.2.75 subvariant, according to CBS News.
The CDC estimates that BN.1 is doubling in proportion roughly every two weeks, though there is a higher degree of uncertainty for this figure, since its overall prevalence is still so low, Natalie Thornburg, PhD, a lead research microbiologist at the CDC, said in a Nov. 12 webinar hosted by the Infectious Disease Society of America. The strain is most prevalent in the West, where it accounts for an estimated 6.2 percent of new cases, CDC data shows.