Future Tense

What We Know About “Stealth Omicron”

Two people in suits watch two people in white lab coats working with equipment.
French Prime Minister Jean Castex and French Health Minister Olivier Véran visit a laboratory that specializes in sequencing at Hôpital de la Croix-Rousse in Lyon on Dec. 3. Jean-Philippe Ksiazek/Getty Images

The omicron wave is beginning to slow in some parts of the country (though hospitals in many places remain overwhelmed). But you may have recently heard about a new member of the COVID cast: BA.2, a relative of omicron. This new relative of the variant we’ve all gotten to know is popping up in dozens of countries, and its nickname, “stealth omicron,” is causing alarm for some; tabloids in the U.K. are getting particularly fearmongery about it. But how much do you really need to worry about it? So far, not much. Here’s what we know.


What’s with this “stealth” business?

According to Peter Chin-Hong, an infectious disease specialist at the University of California, San Francisco, it’s not called “stealth omicron” because a diagnostic PCR test won’t detect it. Rather, it’s “stealth” because it’s a little tricky to determine its lineage—that is, how it relates to other variants. BA.2 is a sublineage of the omicron variant, but it has a specific quirk in its genome (it doesn’t have what’s called an “S-gene deletion”) that can confound some sequencing methods. That means it’s hard to identify as the BA.2 sublineage, not that it’s hard to identify as SARS-CoV-2. PCR tests should still be able to determine if someone is infected with SARS-CoV-2.


Where has it been found?

A lot of our early information is coming out of Denmark, which has a more robust sequencing program than the United States. It’s also been found in more than 50 other countries, like the United Kingdom, India, Sweden, and Singapore, and may be responsible for a rise in cases in Hong Kong. BA.2 has made its way to the United States, with recent reports of its detection coming out of California, Texas, Connecticut, and Washington state.

Is it more contagious than “regular” omicron?

It’s still too early to know for sure, but reports from the Danish government and its top infectious disease authority, the Statens Serum Institut, suggest that BA.2 could be 1.5 times more contagious than omicron. Emphasis on could.


Does it cause more severe disease? Or less severe disease?

It’s also too early to know for sure, but another report from the Statens Serum Institut didn’t show a difference in the risk of hospitalizations from BA.2.

How is it different from original-flavor omicron?

BA.2 has yet another new collection of mutations in the spike protein, the part of the virus that it uses to enter human cells. It also has the aforementioned S-gene deletion.

Will vaccines and therapies still work?

It depends on what you mean by “still work.” According to Chin-Hong, BA.2 “probably follows the omicron playbook, but with an asterisk—we’re not really sure exactly yet.” He said he wouldn’t be surprised if people who have had omicron can still get sick with BA.2, but “I feel very confident that boosters will keep people away from the hospital” because they can be adapted to combat new variants. He also expects antiviral treatments like Paxlovid to still work because they target a different part of the virus (not the spike protein that changes with every new variant). However, it’s unclear whether current monoclonal antibodies will be as efficacious because they do target the spike protein. (Recently the Food and Drug Administration revoked emergency authorization for two monoclonal antibody treatments, those by Regeneron and Eli Lilly, because they are no longer sufficiently effective against omicron.)

What do I do?

Chin-Hong didn’t mince words: “Get your booster.” A booster shot will help keep you out of the hospital if you do get sick—from any variant currently circulating. Additionally, you should keep wearing a mask in crowded situations, and stay home if you test positive or if you think you might be sick. Essentially, every precaution for omicron still stands, and BA.2 is a reminder to get your booster shot as soon as possible.

Future Tense is a partnership of SlateNew America, and Arizona State University that examines emerging technologies, public policy, and society.