The Centers for Disease Control and Prevention is now separately tracking several new COVID-19 variants, the agency announced Friday, adding more Omicron descendants to an increasingly complex list of new strains that are competing nationwide.
Among the new variants now being tracked by the CDC is EU.1.1, a strain first designated by scientists earlier this year over its rapid ascent in some European countries.
The variant is a more distant descendant of the XBB.1.5 variant that had surged earlier this year, with a handful of more mutations to its spike protein that may be driving its spread.
The CDC estimates that EU.1.1 is now 1.7% of U.S. cases nationwide, but may have already reached as much as 8.7% of cases in the region spanning Colorado, Montana, North Dakota, South Dakota, Utah and Wyoming.
It is too early to know whether EU.1.1 will lead to new or different symptoms in the U.S.
Despite some anecdotal reports, health officials have said there's little evidence of previous variants leading to changes in COVID-19's effects. Changes over time in the underlying immunity of those infected can have an impact on how people are affected by the virus, further muddying reports of shifts in symptoms.
Virtually all Americans are now estimated to have antibodies from a vaccination, at least one infection or some combination of the two. A growing share of hospitalizations and deaths are now from reinfections, the CDC reported Thursday.
Laboratories in Utah have sequenced the most EU.1.1 infections of any state, with nearly 100 cases of EU.1.1 reported by the state's public health laboratory to global virus databases.
By contrast, labs in neighboring Nevada and Colorado have reported only single-digit numbers of EU.1.1 sequenced infections.
However, Utah's overall COVID-19 trends currently look similar to the rest of the country, which is currently around record low levels seen during previous spring and summer months.
A consortium of academic and federal modelers recently projected that the U.S. would likely continue to see lulls in COVID-19 hospitalizations and deaths during the warmer months of at least the next two years, with subsequent peaks during the fall and winter unlikely to surpass previous records.
The pace of new COVID-19 hospital admissions and emergency room visits in Utah have largely slowed or plateaued over the past few months, according to CDC figures. Reported nursing home cases there also remain far lower than past winter peaks.
Most variants nationwide are still grouped by the CDC into one of four strains within the XBB family of SARS-CoV-2 variants.
The largest is XBB.1.5, which has fallen to a projected 27.0% of infections. Another is XBB.1.9.2 and XBB.1.9.1, which together make up 24.4% of cases. XBB.1.16 is the next largest, at 19.9% of circulating viruses. Below them is XBB.2.3, at 10.6% nationwide.
The Food and Drug Administration decided earlier this month that COVID-19 vaccines this fall should be revised to target the XBB.1.5 variant. But officials say all these strains, as well as a myriad of their direct descendants, appear to be so closely related that the new shots will broaden immunity for all of them.
Moderna announced Thursday it had already formally completed its submission for emergency use authorization of its newly revised shots for the fall.
While officially designed to target XBB.1.5, the drugmaker touted research suggesting its new vaccine would offer "robust human immune responses" effective at protecting against its relatives XBB.1.16 and XBB.2.3 as well.
CBS News reporter covering public health and the pandemic.