A new COVID Delta offshoot that scientists have voiced concerns about as it spreads through the U.K. has also been detected in the U.S.
However, there have only been three U.S. cases reported and it does not appear to have been spreading recently in the states.
Delta has branched off into dozens of different types that are referred to with the 'AY' label.
One particular Delta AY variant has sparked calls for investigation after rising sharply in the United Kingdom from July onwards, according to the Outbreak.info website that tracks the spread of variants.
It's a version of the AY.4 Delta variant—AY.4 already accounts for around 80 percent of recent cases in the U.K. Now, scientists have noticed an offshoot of the AY.4 variant, an offshoot of an offshoot, that includes a spike mutation known as Y145H and A222V.
Cornelius Roemer, a bioinformatics scientist, named the new Delta offshoot AY.4.2.
In the U.K. it has accounted for around seven to eight percent of new sequenced cases in recent days and about one percent of total cases, Outbreak.Info shows.
Dr. Scott Gottlieb, former commissioner of the U.S. Food and Drug Administration (FDA) from 2017 to 2019, took note of the variant in a tweet on Sunday and said it had been increasing in prevalence since about July.
He wrote: "We need urgent research to figure out if this Delta plus is more transmissible, has partial immune evasion?
"There's no clear indication that it's considerably more transmissible, but we should work to more quickly characterize these and other new variants."
AY.4.2 remains very rare in the U.S., where only three sequences have been recorded. In the U.K. by comparison, there had been 14,247 sequences as of October 18.
It has only been detected in the following locations, Outbreak.Info shows: North Carolina, California, and the District of Columbia, where there has only been one case in each.
Professor Christina Pagel from the Department of Mathematics at University College London (UCL) has noted on Twitter that AY.4.2 is "not growing anywhere near as fast as Delta did" and said the variant is "something to keep an eye on but not panic over."
She added that continuing high cases of Delta in countries like the U.K. are giving it "plenty of opportunities" to keep mutating into new subtypes.
Professor Francois Balloux, director of the genetics institute at UCL, tweeted on Saturday that the Y145H mutation is not an obvious candidate for COVID advantages like immune escape or increased transmissibility but "it feels worthwhile keeping an eye on it."
Correction 6:51 a.m. EDT 10/20/2021: The article has been updated to correct where AY4.2. has spread in the U.S. and how many sequences have been recorded in the U.K.