The Omicron variant quickly took over as the primary driver of COVID-19 infections in the U.S. soon after it was named a variant of concern in late November by the World Health Organization. But a sub-variant of Omicron, called BA.2 or “stealth Omicron” has also been making waves more recently.
According to a CNBC report, BA.2 has caused at least 127 COVID-19 cases in at least half of states in the U.S., but it’s spreading more rapidly in other areas. In Denmark, for example, BA.2 is responsible for almost half of COVID-19 cases in the country, according to governmental research institute Statens Serum Institut.
While public health officials in the U.S. are keeping an eye on stealth Omicron, they aren’t sounding the alarm just yet—they’re largely focused on the main Omicron strain and subsequent Omicron symptoms circulating in the U.S., aka BA.1. Centers for Disease Control and Prevention (CDC) spokesperson Kristen Nordlung told The Washington Post last week that “currently, there are insufficient data to determine whether the BA.2 lineage is more transmissible or has a fitness advantage over the BA.1 lineage.”
But what is BA.2, what are its symptoms, and how transmissible is it? Infectious disease experts break it down.
What is BA.2, or Stealth Omicron?
Omicron has branched into three lineages, explains Thomas Russo, M.D., professor and chief of infectious disease at the University at Buffalo in New York: BA.1, BA.2, and BA.3. Because BA.1 has spread the most rapidly around the world, it’s gotten the most attention, Dr. Russo says—but BA.2 is starting to gain steam, too. (BA.3, which is pretty rare, seems to be a mix of BA.1 and BA.2 that infected the same person at the same time, scrambling their viral genes in the process.)
There’s not a ton known about BA.2 at the moment, but the WHO says it has some differences from BA.1, including some changes in the spike protein, which is what the virus uses to infect your cells. BA.2, though, “is increasing in many countries,” the WHO says online. “Investigations into the characteristics of BA.2, including immune escape properties and virulence, should be prioritized independently (and comparatively) to BA.1,” the agency added.
As for the “stealth Omicron” nickname, experts say it’s not exactly accurate. BA.1, aka the Omicron that people have largely been tracking, is missing one of three target genes that are used in a standard PCR test, Dr. Russo explains. So, when doctors look at testing results, they’ve usually been able to see that someone is infected with the Omicron variant just by spotting the absence of that particular target gene.
But BA.2 doesn’t have the particular mutation on the spike protein that makes that particular target gene fail on a PCR test. Some people started calling it “stealth Omicron” as a result, even though PCR tests would still come up positive for COVID-19 and show all three target genes like they did before Omicron surfaced. FWIW, it’s a controversial nickname that not everyone is into. “Stop calling it stealth Omicron,” says infectious disease expert Amesh A. Adalja, M.D., a senior scholar at the Johns Hopkins Center for Health Security.
What are the symptoms of BA.2?
So far, they seem to be “fairly consistent with known COVID symptoms and not distinguishable from BA.1,” Dr. Adalja says. According to the CDC, those symptoms include:
- Fever or chills
- Shortness of breath or difficulty breathing
- Muscle or body aches
- New loss of taste or smell
- Sore throat
- Congestion or runny nose
- Nausea or vomiting
However, a CDC report released in mid-December found that Omicron in general seems to cause these symptoms:
- Runny nose
How transmissible is BA.2?
Research into BA.2 and its infectiousness is still ongoing, but “BA.2 is likely more transmissible than BA.1 based on it supplanting BA.1 in certain geographic areas,” Dr. Adalja says. “There will always be evolution of this virus towards heightened transmissibility,” he adds.
One analysis of BA.2 conducted by the British government found that the variant is spreading faster than BA.1 because it’s more transmissible. However, it still makes up a very small portion of COVID-19 cases in that country—and in the U.S.
“There is some suggestion that BA.1 may be a little bit more transmissible than Omicron but, at this point, it doesn’t seem to cause any more or less severe disease,” Dr. Russo says.
How worried should you be about BA.2?
Experts say you shouldn’t stress about this variant. “There is no cause for concern with BA.2 as everything you do to handle BA.1 is applicable,” Dr. Adalja says. That means being fully vaccinated against COVID-19 (and getting your booster shot when you’re eligible) and wearing a mask in indoor spaces will help protect you against it.
Dr. Russo doesn’t anticipate that the recent Omicron wave of COVID-19 cases will be heightened much by BA.2. “It’s not like this variant has increased ability to evade vaccine-induced immunity,” he says. “I would also predict that there would be significant protection with BA.2 if you had BA.1. I don’t see this moving the dial significantly in terms of posing a new, huge problem.”
He adds, “there’s not the same concern level that we had with Omicron with BA.1.”
Dr. Adalja agrees. “BA.2 may extend the Omicron wave a little longer, but I don’t think it changes the overall trajectory of the pandemic,” he says.
This article is accurate as of press time. However, as the COVID-19 pandemic rapidly evolves and the scientific community’s understanding of the novel coronavirus develops, some of the information may have changed since it was last updated. While we aim to keep all of our stories up to date, please visit online resources provided by the CDC, WHO, and your local public health department to stay informed on the latest news. Always talk to your doctor for professional medical advice.
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