**Related Video Above: The latest on omicron variant vaccine research.**

(WJW) — A new version of the omicron variant is here. Already seen in Europe and Asia, the subvariant BA.2 has reportedly now made its way to the United States.

Called “stealth omicron” by scientists — due to the fact it’s more challenging to detect as omicron in PCR tests, as one doctor told FOX 8 sister station CBS17 — not a lot is yet known about whether the subvariant is more contagious or causes more severe illness than the BA.1 version of the highly-contagious virus.

So far, Denmark appears to have the most reported cases of BA.2 (with more than 6,400 genome sequences reported to the GISAID Initiative last week), but at least 40 countries have reported appearances of stealth omicron since November, according to the United Kingdom.

“While the BA.1 lineage has previously been the most dominant, recent trends from India, South Africa, the United Kingdom, and Denmark suggest that BA.2 is increasing in proportion,” the World Health Organization explained in a recent brief. “Drivers of transmission and other properties of BA.2 are under investigation but remain unclear to date.”

So where have we seen stealth omicron in the U.S. so far? Among some, researchers at Houston Methodist Hospital in Texas confirmed three cases of BA.2 among COVID patients this month, and the Washington State Department of Health confirmed to FOX 8 they had found two — although those are reported simply as omicron on their website as they said they don’t consider it clinically different.

The U.S. Centers for Disease Control told the Washington Post they are monitoring BA.2, noting it remains a low-circulating form of the virus. Meanwhile, the United Kingdom Health Security Agency (UKHSA) also announced they have designated stealth omicron as a “variant under investigation.”

“It is the nature of viruses to evolve and mutate, so it’s to be expected that we will continue to see new variants emerge as the pandemic goes on,” Dr. Meera Chand, COVID-19 Incident Director at UKHSA, said in a statement. “So far, there is insufficient evidence to determine whether BA.2 causes more severe illness than Omicron BA.1, but data is limited and [we continue] to investigate.”