What is the "delta plus" variant? It's a relative of the delta variant, identified by British scientists last month.
Because it isn't a variant of interest or concern, it has not yet been officially named after a letter of the Greek alphabet, like the other worrisome variants.
Scientists are monitoring the delta-related variant — known as AY.4.2. — to see if it might spread more easily or be more deadly than previous versions of the coronavirus. In a recent report, U.K. officials said this variant makes up 6% of all analyzed COVID-19 cases in the country and is "on an increasing trajectory."
The variant has two mutations in the spike protein, which helps the coronavirus invade the body's cells. These changes have also been seen in other versions of the virus since the pandemic started, but haven't gone very far, Francois Balloux, director of the Genetics Institute at University College London.
The delta variant remains "by far the most dominant variant in terms of global circulation" said Maria Van Kerkhove, the World Health Organization's technical lead on COVID-19, at a public session this week.
"Delta is dominant, but delta is evolving," she said, adding that the more the virus circulates, the greater chances it has to mutate.
The U.N. health agency is currently tracking 20 variations of the delta variant. The AY.4.2 is "one to watch because we have to continuously keep an eye on how this virus is changing," said Van Kerkhove.
In the U.S., the delta variant accounts for nearly all COVID-19 cases. The newer "delta plus" variant has been spotted "on occasion," but it's not yet a concern, health officials said.