The BA.5 variant that dominated the summer wave of COVID-19 infections and hospitalizations has now fallen to 81.3% of new cases, according to estimates released Friday by the Centers for Disease Control and Prevention.
Three rival strains – the BF.7, BA.2.75, and BA.4.6 variants – have now climbed to make up around 1 in 5 new infections nationwide, according to federal estimates.
Data published by the CDC on Thursday tallied just 2% of Americans living in counties rated at "high" COVID-19 Community Levels, where the agency urges indoor masking and other measures to curb the virus.
But health officials have cautioned for weeks that the U.S. was not "out of the woods" yet.
Scientists and health authorities have been bracing for a widely expected resurgence in the virus. The last two winter seasons saw deadly waves sweep the country.
Despite President Bidenthis month that the pandemic had ended, authorities have also urged Americans to seek out updated boosters redesigned to guard against the BA.4 and BA.5 variants.
Around 7.6 million Americans have received the updated shots, or close to 4% of the 209 million people who are eligible for the booster. The pace of new shots in arms has accelerated to the fastest pace in months, CDC data shows, but remains behind last year's rollout of boosters.
One potential candidate for a fall and winter wave now being tracked by virus experts is BA.2.75.2. Early lab data from Europe and China suggests the variant harbors mutations that add up to the most "extreme antibody escape than any variant we've seen so far."
"With the combination of the evolution of variants, as well as the seasonal aspects, that as we get into this coming late fall and winter, it is likely that we will see another variant emerge," Dr. Anthony Fauci, the president's outgoing chief medical adviser, said last week at an event hosted by the Center for Strategic and International Studies.
At least 188 cases of this subvariant have been detected in the U.S. to date across 26 states.
"There's already on the horizon one that looks suspicious that it might start to evolve as another variant, and that's the BA.2.75.2," said Fauci.
The CDC has yet to publish a specific estimate for this strain, since it remains below 1% nationwide, but it has been "gradually increasing over the last few weeks." The variant's umbrella lineage – BA.2.75 – has grown to 1.4% of cases nationwide.
BA.2.75's prevalence is highest right now in the New York and New Jersey region, where the CDC estimates it makes up 2.4% of new infections.
The CDC's airport surveillance has also detected the variant in flights from India, as of August.
BA.4.6 and BF.7
The two other variants – BA.4.6 and BF.7 – have raised concerns because they might evade the protection offered by a key antibody drug used to shield immunocompromised Americans who might not be able to get immunity from vaccination known as Evusheld.
"BF.7 has one additional genetic change in the gene coding for the Spike protein in comparison to parental BA.5 lineage viruses. Data indicates that this specific genetic change could reduce the efficacy of Evusheld," CDC spokesperson Jasmine Reed told CBS News in a statement.
Reed said that so far "there is no indication that vaccines or diagnostic tests" are affected by BF.7's mutations.
The CDC says 3.4% of cases nationwide are now from BF.7. 12.8% are from BA.4.6.
BF.7's proportion is largest in New England, where the CDC says 5.7% of new infections are linked to the variant. The CDC has also detected the variant in passengers flying from France.
New England is also where recent federal hospitalization and nursing home data has tracked an uptick in the virus, at a time when most regions have recorded a steep decline.
After past variants threatened the protection offered by AstraZeneca's drug, the Food and Drug Administration moved to boost the dose of Evusheld to fend off the strains.
It is unclear if the FDA will make a similar move this fall, in response to the new strains.
"The FDA is working with sponsors of all currently authorized therapeutics to assess the activity against any global SARS-CoV-2 variant(s) of interest and is committed to communicating with the public as we learn more," Chanapa Tantibanchachai, a spokesperson for the FDA, said in a statement.