BA.2.12.1, which is estimated to be 23 to 27 percent more transmissible than its predecessor, BA.2, currently accounts for roughly 1 in 5 new cases across America.
The variant is fuelling a resurgence in Covid cases seen in upstate New York, the State Department of Health reported last week.
“BA.2.12.1 has increased rapidly in proportion in the US compared to other BA.2 sublineages,” especially in the region that includes New York and New Jersey, CDC spokesperson Kristen Nordlund told CNN.
Five cases of BA.2.12.1 have also been detected in the UK. Covid Genomics UK Consortium (COG-UK), which monitors the spread of new strains in Britain, says the variant was first picked up on 23 March.
The variant has also been spotted in Australia, Israel, Denmark and Austria.
There’s no evidence to suggest that BA.2.12.1 causes more severe disease than the original Omicron variant and its various spin-offs.
The majority of cases in the US — around 75 percent — are still caused by BA.2, which has been the country's dominant variant since late March.
It’s unclear whether BA.2.12.1 is spreading more quickly than other Omicron sub-variants because it is more contagious or better at evading the body’s immunological defences.
The variant has acquired one mutation of particular interest, called L452Q, in its spike protein — the part of the virus responsible for binding and gaining entry to human cells.
“We're now starting to see the evolution of new potentially impactful sublineages of Omicron,” tweeted Trevor Bedford, a virologist at Fred Hutchinson Cancer Research Center.