Health officials are studying a new version of the Omicron coronavirus variant that has been detected in 40 countries, including Europe, Asia and some parts of the US.

The subvariant is known as BA.2 because the original strain of Omicron was deemed BA.1. The US Centers for Disease Control and Prevention (CDC) said currently there is insufficient data to determine whether the BA.2 lineage is more transmissible or has a fitness advantage over the BA.1 lineage.

Pam Vallely, professor of medical virology at the University of Manchester in England, told Newsweek that she hasn't yet seen any evidence to suggest that BA.2 causes more severe disease than BA.1, adding that "we need a few weeks' more data to analyze".

The subvariant has become more prevalent in the UK and Denmark, where it has been dubbed "stealth Omicron".

"We are not so concerned, since we so far do not see major differences in age distribution, vaccination status, breakthrough infections and risk of hospitalization. Also, despite the high infection rate of BA. 2, the numbers of hospitalizations [in] ICUs are decreasing," Anders Fomsgaard a virologist at the Statens Serum Institut in Denmark, told The Washington Post.

Tom Peacock, a virologist at Imperial College London, said the earliest indications from Denmark and India "suggest there is no dramatic difference in severity compared to BA.1".

Peacock also said: "There is likely to be minimal differences in vaccine effectiveness against BA.1 and BA.2."

The World Health Organization said Monday that BA.2 has different properties that separate it from the Omicron strain and recommended that the investigations continue.

"The BA.2 descendent lineage, which differs from BA.1 in some of the mutations, including in the spike protein, is increasing in many countries," the WHO wrote on its website. "Investigations into the characteristics of BA.2, including immune escape properties and virulence, should be prioritized independently (and comparatively) to BA.1."

Scientists discovered the BA.2 in December, shortly after the original Omicron lineage was identified. Around the world, a total of more than 10,000 cases of BA.2 have been reported, although the number may be an underestimate.

In Europe, BA.2 had "quickly taken hold" in Denmark and made up around half of the European country's Omicron cases, but there was no difference in hospitalizations between the original Omicron and the subvariant, British News outlet Sky News reported Friday.

In Denmark, BA.2 jumped from 20 percent of coronavirus cases in the last week of December to 45 percent of cases in the second week of January, according to the Statens Serum Institut.

As of Monday, BA.2 accounted for around 65 percent of new infections in Denmark. In Norway and Sweden, BA.2 may already be overtaking the original omicron variant, the news site The Hill reported.

There has been a total of 88 reported samples of BA.2 in the US from about 22 states, according to Newsweek, citing the virus sequencing database GISAID.

Washington state's health department on Monday confirmed two cases of the BA.2 have been detected in the state, according to the NBC-TV affiliate in Seattle. At least three cases have been found at Houston Methodist Hospital in Texas, the Post reported.

"Although the BA.2 lineage has recently increased in proportion in some countries, it remains a very low proportion of circulating viruses in the United States and globally," Kristen Nordlund, a spokeswoman for the CDC, told the Post. "CDC continues to monitor variants that are circulating both domestically and internationally."

A Moroccan researcher said that BA.2 belongs to the same lineage as the Omicron variant but has 30 more mutations than the original version. Some of those mutations are on the spike protein, a key part for the virus to enter human cells and the target of some antibodies.

On Monday, more than 695,000 new coronavirus cases were reported in the US, and almost all were from Omicron. The figure is down 13.7 percent from the previous week, according to data tracked by the Post.