Scientists and health officials around the world are keeping their eyes on a descendant of the omicron variant that has been found in more than 50 countries, including the United States.

This version of the coronavirus, which scientists call BA.2, is widely considered stealthier than the original version of omicron because particular genetic traits make it somewhat harder to detect. Danish scientists reported this week that preliminary information suggests it may be 1 1/2 times more contagious then the original variant.

But scientists say therexe2x80x99s a lot they still donxe2x80x99t know about it, including whether it causes more severe disease.

WHERE HAS IT SPREAD?

More than 18,000 genetic sequences of BA.2 have been uploaded to GISAID, a global platform for sharing coronavirus data, according to data collected by Scripps Research labs. The strain has been detected in at least 54 countries and 24 U.S. states.

xe2x80x9cThus far, we havenxe2x80x99t seen it start to gain groundxe2x80x9d in the U.S., said Dr. Wesley Long, a pathologist at Houston Methodist in Texas, which identified three cases as of earlier this week.

The mutant appears much more common in Asia and Europe. In Denmark, it has spread quickly and become the dominant variant, according to State Serum Institute, which falls under the Danish Ministry of Health.

xe2x80x9cPreliminary calculations indicate that BA.2 is one and a half times more contagious than BA.1,xe2x80x9d the original omicron, the institutexe2x80x99s Dr. Tyra Grove Krause said in a press release earlier this week. If it is more contagious, xe2x80x9cit may mean that the wave of infections will be higher and will extend further into February compared to the previous projections.xe2x80x9d

WHATxe2x80x99S KNOWN ABOUT THIS VERSION OF THE VIRUS?

BA.2 has lots of mutations. About 20 of them in the spike protein that studs the outside of the virus are shared with the original omicron. But it also has additional genetic changes not seen in the initial version.

Itxe2x80x99s unclear how significant those mutations are, especially in a population that has encountered the original omicron, said Dr. Jeremy Luban, a virologist at the University of Massachusetts Medical School.

For now, the original omicron BA.1 and its descendant BA.2 are considered subsets of omicron. But global health leaders could give it its own Greek letter name if it is deemed a globally significant xe2x80x9cvariant of concern.xe2x80x9d

Scientists at the UK Health Security Agency found that vaccine effectiveness against symptomatic disease appears similar for BA.1 and BA.2. Looking at all vaccine brands combined, scientists found they were about 70% effective against symptomatic disease from BA.2 two or more weeks after a booster shot.

An initial analysis by scientists in Denmark shows no differences in hospitalizations for BA.2 compared with the original omicron. They are also looking into how well current vaccines work against it. Itxe2x80x99s also unclear how well treatments will work against it.

Doctors also donxe2x80x99t yet know for sure if someone whoxe2x80x99s already had COVID-19 caused by omicron can be sickened again by BA.2. But theyxe2x80x99re hopeful, especially that a prior omicron infection might lessen the severity if that happens.

The two versions of omicron have enough in common that itxe2x80x99s possible that infection with the original mutant xe2x80x9cwill give you cross-protection against BA.2,xe2x80x9d said Dr. Daniel Kuritzkes, an infectious diseases expert at Brigham and Womenxe2x80x99s Hospital in Boston.

Scientists will be conducting tests to see if antibodies from an infection with the original omicron xe2x80x9care able to neutralize BA.2 in the laboratory and then extrapolate from there,xe2x80x9d he said.

HOW CONCERNED ARE HEALTH AGENCIES?

The World Health Organization classifies omicron overall as a variant of concern, its most serious designation of a coronavirus mutant, but it doesnxe2x80x99t single out BA.2 with a designation of its own. Given its rise in some countries, however, the agency says investigations into its characteristics xe2x80x9cshould be prioritized.xe2x80x9d

The UK agency, meanwhile, has designated BA.2 a xe2x80x9cvariant under investigation,xe2x80x9d citing the rising numbers found in the U.K. and internationally.

WHY IS IT HARDER TO DETECT?

The original version of omicron had specific genetic features that allowed health officials to rapidly differentiate it from delta using a certain PCR lab test because of whatxe2x80x99s known as xe2x80x9cS gene target failure.xe2x80x9d

BA.2 doesnxe2x80x99t have this same genetic quirk. So on the test, Long said, it looks like delta.

xe2x80x9cItxe2x80x99s not that the test doesnxe2x80x99t detect it; itxe2x80x99s just that it doesnxe2x80x99t look like omicron,xe2x80x9d he said.

WHAT SHOULD YOU DO TO PROTECT YOURSELF?

Doctors advise the same precautions they have all along: Get vaccinated and follow public health guidance about wearing masks, avoiding crowds and staying home when youxe2x80x99re sick.

xe2x80x9cThe vaccines are still providing good defense against severe disease, hospitalization and death,xe2x80x9d Long said.

The latest version is another reminder that the pandemic hasnxe2x80x99t ended.

xe2x80x9cWe all wish that it was over,xe2x80x9d Long said, xe2x80x9dbut until we get the world vaccinated, wexe2x80x99re going to be at risk of having new variants emerge.xe2x80x9d

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institutexe2x80x99s Department of Science Education. The AP is solely responsible for all content.