Stealth Omicron Sub-Variant BA.2 Found in Almost Half of U.S. States

Almost 100 cases of the Omicron sub-variant BA.2 have been detected in the U.S. across more than 20 states, virus genetic data shows.

According to the virus database GISAID, which scientists can use to share sequenced COVID samples from around the world, 92 BA.2 cases had been reported from the U.S. by about 5:15 a.m. ET on Tuesday.

The cases were reported from about 22 states, including Arizona, California, Texas and Washington. It should be noted that the figures are updating frequently and are subject to change.

Washington news outlet KOMO News reported on Monday that the state's department of health had confirmed two cases of the sub-variant there and noted there were about 100 confirmed cases in the country.

Experts say it's too early to know whether BA.2 will cause a difference in disease severity compared to BA.1, though Cornelius Roemer, a computational biologist at the Univeristy of Basel in Switzerland, called it "the Omicron sibling to watch" in a tweet on Monday. He added that it had been "picking up pretty much everywhere I've looked".

Eric Feigl-Ding, an epidemiologist at the Federation of American Scientists, tweeted on Thursday that there are concerns about reinfection with BA.2 even in people who recently had a BA.1 Omicron infection—something referred to as a theoretical possibility by Anders Fomsgaard, chief physician and virus researcher at Denmark's Statens Serum Institut (SSI), in an interview with Danish news outlet TV2 last week.

Cases of BA.2 are relatively low in the U.S. compared to western Europe, where it now accounts for thousands of COVID cases.

In Denmark, the sub-variant accounted for just under half of recent national cases according to the SSI on January 20.

The U.K. has also reported several hundred cases, though compared to Denmark these appear to be much lower in proportion to the BA.1 Omicron variant that has previously been dominant around the world.

In a technical brief published on January 21, the World Health Organization noted that BA.2 also appeared to be increasing in proportion in India and South Africa, according to recent trends, and wrote: "Drivers of transmission and other properties of BA.2 are under investigation but remain unclear to date."

Some experts say there is currently not enough evidence to understand how much concern is warranted by BA.2, since it isn't known whether it causes a difference in disease severity compared to BA.1.

Further Analysis Needed

The U.K. Health Security Agency (HSA) stated on Friday that early analysis suggests BA.2 may have an increased growth rate compared to BA.2, but that this wasn't certain and further analysis was needed.

"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," said Dr. Meera Chand, COVID incident director at the HSA. "Our continued genomic surveillance allows us to detect them and assess whether they are significant."

The variant is sometimes referred to as "stealth Omicron." It is detected via tests, but not in the same way as the previous Omicron variant.