What is known about the “stealth” version of omicron?

Washington Hispanic:

Scientists and health officials around the world are keeping an eye on a descendant of the omicron variant that has been found in at least 40 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. Some scientists worry that it may also be more contagious.

But they say there’s a lot they still don’t know about it, including whether it better evades vaccines or causes more serious disease.


Since mid-November, more than three dozen countries have uploaded nearly 15,000 BA.2 genetic sequences to GISAID, a global platform for sharing coronavirus data. As of Tuesday morning, 96 of those sequenced cases were from the United States.

“So far, we haven’t seen it start to gain traction” in the United States, said Dr. Wesley Long, a pathologist at Houston Methodist in Texas, who has identified three cases of BA.2.

The mutant seems much more common in Asia and Europe. In Denmark, it accounted for 45% of all COVID-19 cases in mid-January, up from 20% two weeks earlier, according to the Statens Serum Institut, which reports to the Danish Health Ministry.


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

It’s not clear how significant those mutations are, especially in a population that has found the original omicron, said Dr. Jeremy Luban, a virologist at the University of Massachusetts Medical School.

For now, the original version, known as BA.1, and BA.2 are considered subsets of omicron. But world health leaders could give it its own Greek-letter name if it’s deemed a “variant of concern” of global importance.

The rapid spread of BA.2 in some places raises concerns that it could take off.

“We have some indications that it may be as contagious or maybe a little more contagious than the (original) omicron, as it is able to compete with it in some areas,” Long said. “But we don’t necessarily know why that is.”

An initial analysis by scientists in Denmark shows no difference in BA.2 hospitalizations compared to the original omicron. Scientists are still investigating the infectivity of this version and how well current vaccines against it work. It’s also unclear how well treatments will work against it.

Doctors still don’t know for sure if someone who has already had COVID-19 caused by omicron can get sick from BA.2 again. But they are hopeful, especially that a previous omicron infection might lessen the severity of the disease if someone later gets BA.2.

The two versions of omicron have enough in common that it’s possible that infection with the original mutant “gives you cross-protection against BA.2,” said Dr. Daniel Kuritzkes, an infectious disease expert at Brigham and Women’s Hospital.

Scientists will test to see if antibodies from an infection with the original omicron “are able to neutralize BA.2 in the lab and then extrapolate from there,” he said.


The World Health Organization classifies omicron overall as a variant of concern, its most serious designation of a coronavirus mutant, but does not single out BA.2 with a designation of its own. However, given its rise in some countries, the agency says investigations of BA.2 “need to be prioritized.”

Meanwhile, the UK Health Security Agency has designated BA.2 as a “variant under investigation”, citing the growing number found in the UK and internationally. Still, the original version of omicron remains dominant in the UK.


The original version of omicron had specific genetic characteristics that allowed health officials to quickly differentiate it from delta using a certain PCR test due to what is known as “S-gene target failure.”

BA.2 does not have this same genetic peculiarity. So on test, Long said, BA.2 looks like delta.

“It’s not that the test doesn’t pick it up; it just doesn’t look like omicron,” he said. “Don’t be under the impression that ‘stealth micron’ means we can’t detect it. All of our PCR tests can still detect it.”


Doctors advise the same precautions they take all the time: Get vaccinated and follow public health guidelines about wearing masks, avoiding crowds and staying home when you’re sick.

“Vaccines continue to provide a good defense against severe illness, hospitalization and death,” Long said. “Even if you’ve had COVID 19 before, you’ve had a natural infection, the protection from the vaccine is still stronger, longer lasting and actually… does good for people who have been previously infected.”

The latest version is another reminder that the pandemic is not over.

“We all wish it would end,” Long said, “but until we vaccinate the world, we’re going to be at risk of new variants emerging.”