What To Know About BA.2, the 'Stealth' Omicron Variant

The SARS-CoV-2 virus has mutated several times since the start of the COVID-19 pandemic. The World Health Organization reported in February 2022 that another version of the Omicron variant of COVID-19 was increasing in many countries—and the organization urged researchers to investigate whether the strain posed any new threats to the state of the pandemic.

The version, known as BA.2, is a descendant of the Omicron variant (known as BA.1). According to the WHO, BA.2 has some differences in some of its mutations—including ones on the spike protein—compared to BA.1. Those differences, along with BA.2's increasing spread in some areas, led the WHO to recommend investigations into the characteristics of BA.2.

What Is BA.2?

The BA.2 version of Omicron is technically a descendant of the original (BA.1) Omicron variant. It was designated a "variant under investigation" by the United Kingdom Health Security Agency (UKHSA) on January 21, 2022, due to "increasing numbers of BA.2 sequences identified both domestically and internationally," according to a news release.

According to Statens Serum Institut (SSI), Denmark's governmental research institute, BA.2 has some genetic differences compared to BA.1 in "the most important areas". The SSI said "the difference between BA.1 and BA.2 is greater than the original [SARS-CoV-2] and the Alpha variant," and those differences could mean differences in "infectiousness, vaccine efficiency, or severity."

The Spread of BA.2

In early 2022, the variant was most prominent (at least by way of testing) in Denmark—nearly half of all Danish cases of Omicron were due to BA.2 at that time, according to SSI. According to the UKHSA, after Denmark, most sequences of BA.2 were initially found in India, Sweden, and Singapore.

By January 2022, it was reported that "more than 100 cases" had been detected in the United States across 20 states, according to data from GISAID, an open-access genetic sequencing database.

Why Was BA.2 Called 'Stealth Omicron'?

According to a January 24, 2022, article in The Washington Post, some scientists gave BA.2 the nickname "stealth Omicron," with the claim that it has certain genetic traits that make it more difficult to identify as Omicron on diagnostic tests—specifically polymerase-chain-reaction (PCR) tests.

But that "stealthiness" doesn't mean the virus itself goes undetected—just that it's harder to classify as Omicron, John Sellick, DO, an epidemiologist and professor of medicine at the University at Buffalo/SUNY, told Health.

When the original Omicron variant shows up on a PCR test, it can be quickly identified, due to a genetic deletion in the virus' spike protein—this elicits what's known as an "S-gene target failure" in some PCR tests, which allowed researchers to accurately identify the virus as Omicron, according to the UKHSA. BA.2 doesn't have that genetic deletion, which makes it harder to detect and classify as Omicron on those tests.

In that case—because BA.2 isn't evading detection, just classification—its "stealth Omicron" nickname is "illogical," Gary Whittaker, PhD, professor of virology at Cornell University, told Health.

Ultimately, Dr. Sellick said the "stealth Omicron" nickname may be helpful for scientists in a laboratory setting, but not so much in a clinical manner—meaning it won't change the results of your positive COVID-19 test or the care you'd receive.

Is BA.2 a Cause For Concern?

Initial research conducted by the SSI showed no differences in the hospitalization rates for BA.2 as compared to BA.1. And while further research needs to be done on how the Omicron versions differ in transmissibility and vaccine efficiency, the institute said at the time "it is expected that vaccines also have an effect against severe illness upon BA.2 infection."

According to the CDC COVID-19 data tracker, the rates of infections caused by the BA.2 variant declined after the first few months of 2022, and other variants began to emerge.

COVID-19 Variants

BA.2 aside, Perry Halkitis, PhD, professor of epidemiology at Rutgers School of Public Health, said at the time that this subvariant—along with the previous variants and any more to come—are expected. "We're going to continue to see mutations throughout the course of our history around COVID because we haven't completely eradicated the virus," Dr. Halkitis added.

One factor is the number of people who are still unvaccinated. "We have too many people [who are] unvaccinated," Dr. Sellick said. "It's letting this virus multiply and replicate a lot. These mutations are just going to continue to crop up and give us new variants."

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.