Scientists are keeping a close watch on a recently-discovered sub-variant of the Omicron variant of the coronavirus to determine how its emergence could affect future pandemic spread.

The initial Omicron variant has become the dominant virus strain in recent months but British health authorities have notably identified hundreds of cases of the latest version, dubbed BA.2, while international data suggest it could spread relatively quickly.

The UK Health Security Agency (UKHSA) identified more than 400 cases in Britain in the first 10 days of this month and has indicated the latest variant has been detected in some 40 other countries, accounting for a majority of most recent cases in some nations including India, Denmark and Sweden.

The UKHSA indicated on Friday it had designated the BA.2 sub-lineage as a variant under investigation (VUI) as cases of it were on the increase even if, in Britain, the BA.1 lineage currently remains dominant.

The authority underlined that “there is still uncertainty around the significance of the changes to the viral genome”, which required surveillance as, in parallel, cases in recent days showed a sharp rise in BA.2 incidence notably in India and Denmark.

“What surprised us is the rapidity with which this sub-variant, which has been circulating to a great extent in Asia, has taken hold in Denmark,” French epidemiologist Antoine Flahault told the AFP news agency.

Scientists must evaluate how the virus continues to evolve and mutate. Its latest incarnation does not possess the specific mutation used to track and compare BA.1 with Delta, the previously dominant strain.

BA.2 has yet to be designated a variant of concern – but Flahault says countries have to be alert to the latest development as scientists ramp up surveillance.