NEW YORK, Feb. 23 (UPI) -- A new, potentially more contagious and threatening strain of Omicron, BA.2, is spreading in the United States and may threaten efforts to relax COVID-19 pandemic-related restrictions across the country.

The strain has led to a rapid increase in cases in Denmark, which moved to relax pandemic restrictions in recent days, according to the World Health Organization. Brunei, Georgia and Nepal also are experiencing significant outbreaks.

And while the numbers in the United States are small, medical detectives are keeping a close watch on trends.

Fewer than 1,400 cases involving the new subvariant have been reported in this country, according to outbreak.info, which is supported by the Centers for Disease Control and Prevention and other major research groups. That's less than 0.5% of cases reported since BA.2 appeared.

Dubbed the "stealth variant" because it appears to be more difficult to detect than earlier strains of the virus that causes COVID-19, BA.2 has been found to be more transmissible and perhaps less responsive to vaccines and treatments than its predecessors, WHO says.

"There's not a lot of information that we have on this particular subvariant yet," Maria Van Kerkhove, WHO technical lead on COVID-19, said during a press conference earlier this month.

However, "because it is part of this package of Omicron, we do know obviously that there is increased growth rate compared to other variants of concern," she said.

Increased transmission

As the surge in COVID-19 cases fueled by the emergence of the Omicron variant begins to fade across much of the United States, states continue to relax restrictions designed to limit the spread of the virus, including the requirement that people wear masks in indoor public spaces.

Only Hawaii retains an indoor mask mandate, and many experts are concerned that governments are loosening the reins on these restrictions too soon.

That's because BA.2 is about 30% more contagious than BA.1 and it "possesses immune-evasive properties that further reduce the protective effect of vaccination against infection," according to data released Jan. 31 by the Staten Serum Institute, Denmark's agency for infectious disease response.