After COVID-19 cases in the U.S. came down from their January peak, those numbers are climbing yet again. This time experts say the increase is likely due to a new variant called BA.2, a subvariant of omicron that's nicknamed the “stealth” variant.
This new coronavirus variant appears to be steadily replacing the original omicron. In fact, BA.2 has been the dominant coronavirus strain in the U.S. since mid-March, according to the latest estimates from the Center for Disease Control and Prevention. The subvariant was responsible for an estimated 75% of COVID-19 cases in the country as of April 16.
"As we’ve previously shared about the BA.2 variant, there is no evidence that BA.2 results in more severe disease compared with the BA.1 variant (omicron), nor does it appear to be more likely to evade immune protection than BA.1. But BA.2 does appear to be more transmissible than BA.1," CDC director Dr. Rochelle Walensky said in a recent White House press briefing.
"The high level of immunity in the population from vaccines, boosters, and previous infection will provide some level of protection against BA.2," she explained. "However, we strongly encourage everyone to be up to date on their COVID-19 vaccines."
Other subvariants are picking up steam as well
The only thing slowing down BA.2's takeover appears to be the emergence of even more omicron-related subvariants. These new variants, called BA.2.12.1 and BA.2.12, are picking up steam. And BA.2.12.1 is now responsible for an estimated 20% of all COVID-19 cases in the country, NBC News reported.
In New York state, health officials say these new subvariants may be behind the significant uptick in local cases over the past few weeks. During March, those two subvariants accounted for more than 70% of the COVID-19 cases in Central New York and are now responsible for more than 90% so far in April, the state health department said.
Officials estimated that the new subvariants are between 23% and 27% more transmissible than BA.2, which experts have already said was about 30% more transmissible than the original omicron strain. But, so far, there's no evidence that the new variants cause more severe disease.
“We are alerting the public to two omicron subvariants, newly emerged and rapidly spreading in upstate New York, so New Yorkers can act swiftly,” state health commissioner Dr. Mary T. Bassett said in a press release. “While these subvariants are new, the tools to combat them are not."
She went on to urge people to get fully vaccinated and boosted, to get tested for COVID-19 when appropriate, and to consider masking up — especially in indoor public spaces.
What makes the BA.2 variant different?
BA.2 is actually a subvariant of the omicron strain.
“The original omicron is dramatically different than anything else before it, so we’re not talking about the shift between delta and omicron,” Dirk Dittmer, Ph.D., professor in the department of microbiology and immunology at the University of North Carolina School of Medicine, told TODAY.
“I think what we’re seeing here is a drift where some of the mutations that the original omicron had are gone and others have been added,” he said.
Those mutations could be worrisome if they turn out to affect any of three key areas: disease transmission, severity of disease and the variant’s ability to evade immunity, Dr. Albert Ko, epidemiology professor at Yale School of Public Health, told TODAY. In particular, BA.2 appears to spread more easily than omicron, he said.
Even the earliest data suggested that BA.2 is more transmissible than previous variants — including omicron. By Jan. 20, BA.2 accounted for 45% of Denmark’s COVID-19 cases, which was up from 20% two weeks before, according to surveillance data. Experts say that level of transmissibility is what’s led this variant to become dominant in the U.S., as well.
Does the BA.2 variant cause more severe COVID-19 disease?
Data so far indicate that BA.2 isn’t likely to cause more severe disease than omicron.
In areas of the world where BA.2 is taking over, “you’re not seeing large increases in hospitalizations and deaths,” Ko said. “So that kind of reassures us that it may not be more virulent. But we really need much more waiting, much more rigorous data,” he said.
“The true answer is: No one knows because they just finished sequencing (the variant),” Dittmer said. According to the one published report from Denmark, the BA.2 variant appears to be more transmissible than omicron but no less severe, he said, “but that’s like three weeks’ worth of observations.”
It will take at least a few more weeks for other research to corroborate those findings in other parts of the world, Ko explained.
One worrying finding so far is that many of the antibody treatments doctors have used to treat COVID-19 infections in the past don't seem to be helpful against infections caused by omicron. And the situation with BA.2 might be even worse: A study looking at the BA.1 and BA.2 variants in a laboratory setting found that another antibody therapy — sotrovimab — may be effective against BA.1 but not against BA.2.
The study, which was posted to a preprint server and has not yet been peer-reviewed, also found that AstraZeneca's preventive antibody cocktail Evushield was effective against BA.1 but not with BA.2.
However, the Food and Drug Administration said that a newly authorized antibody treatment, bebtelovimab, is effective in managing both omicron and BA.2.
Should we expect another surge in cases due to BA.2?
It’s unlikely that we’ll see another major surge due to BA.2, but the emergence of this variant may result in “prolonged transmission” of the current omicron wave, Ko said. “This may not be the sharp up and down” that some had predicted we would see with omicron, he explained.
Dittmer agreed that we aren’t likely to see another major wave in cases due to this variant shift, but he also said it’s too early to know whether we would see a prolonging of the current wave. “If you look at all the other variants, they cycle in four- to six-month intervals,” he explained. “We’re still in the middle of one peak and we’re coming down, but whether that gets prolonged or not — that’s what no one knows.”
Why is BA.2 nicknamed the “stealth” variant?
This part of the story is a little complicated: PCR tests use three primers to detect the coronavirus. With omicron, only two would react, Ko explained. So PCR tests could reliably pick up omicron and, because omicron would appear differently on the test, there was a shortcut to identifying those cases as being caused by that particular variant.
But BA.2 does not appear to have this same quirk that omicron had. That means BA.2 cases will still show up on a PCR test, but they’ll show up the way previous variants did. “What you lose with BA.2 is the ability to say — based on the PCR test alone — that it’s delta or omicron,” Dittmer said, adding that labs should really only rely on actual genetic sequencing to make that determination anyway.
What can you do to protect yourself against the BA.2 variant?
"If cases rise from the omicron variant or any other variant, we have the tools — vaccines, boosters, tests and therapeutics — to be prepared," Walensky said. "From a public health standpoint, it is critical that we continue to provide people with the tools to keep them, their families and their communities safe."
As individuals, there’s not much more you can do than follow the public health guidelines you are already familiar with, Dittmer said. That includes getting vaccinated if you haven’t already, getting boosted if you’re eligible, continuing social distancing and wearing a mask (ideally a KN95 or N95) when interacting with others.
If you’re still using a cloth or surgical mask or even if you’re double-masking, now is the time to upgrade, the experts said.
Early data from Denmark indicated that vaccination is crucial. In a study published to a preprint server this week (meaning it has not been peer-reviewed), people were less likely to get and spread the BA.2 variant if they were vaccinated than if they were not vaccinated.
Omicron reinfections are also possible but generally rare, according to a Danish study published in February to a preprint server (meaning it has not been peer-reviewed yet). And, among the 47 participants in the study who had an infection with BA.2 following a previous infection with BA.1, the majority (89%) were unvaccinated.
What can we do to prevent more variants in the future?
The only way to really reduce the chances that more variants might emerge in the future is to prevent transmission of the virus here and around the world. “As long as we maintain a very high level of infections, we’re basically breeding variants,” Dittmer said. “That’s a catchy quote, but it’s actually accurate.”
The fact that we had another variant in omicron wasn’t a surprise, Ko said. But what did surprise experts was that the variant wasn’t related to delta. “What we did learn is that these new variants will emerge in places which will likely have uncontrolled transmission,” Ko explained. That’s why “vaccinating the world is going to be important,” he said. “We can’t leave any part of the world behind.”
Boosters can also play an important role in protecting us from new variants and, hopefully, preventing even more variants. Now that omicron has pretty much completely taken over in the U.S., it’s reasonable to expect the emergence of more variants that are closely related to omicron, such as BA.2.
Keeping that in mind, it makes sense to start thinking about booster shots to protect against omicron specifically, Dittmer said. “I’m hoping that by the end of the year, there’ll be an omicron-specific booster. That would be my dream scenario.”
This article was updated on April 20, 2022 to include updated data about the BA.2 variant and emerging subvariants.