The BA.2 variant has been around for several weeks already, but as cases rise abroad and show signs of spread in parts of the U.S., could the omicron subvariant be one to watch for next?
The BA.2 variant, also known as "stealth omicron," a more transmissible version of the omicron variant, is beginning to grow in parts of the U.S. and is believed to be behind a number of COVID increases in multiple countries.
Now, experts say they're expecting cases will rise, but how much?
Chicago's top doctor said Thursday she is "concerned" by what is happening in other parts of the world.
Here's what we know so far:
What is BA.2?
BA.2, also known as "stealth omicron," is considered a subvariant of omicron.
BA.2 has several key mutations, with the most important of those occurring in the spike protein that studs the outside of the virus. Those mutations are shared with the original omicron, but BA.2 also has additional genetic changes not seen in the initial version.
So far, it has not yet been declared a variant of concern on its own.
"BA.2 is part of omicron," Dr. Isaac Ghinai, medical director for lab-based surveillance at the Chicago Department of Public Health, said Thursday. "Omicron is a variant of concern, therefore BA.2 is a variant of concern. Same as BA.1 is a variant of concern."
But that could change.
"People are looking very closely at whether or not BA.2 needs to be classified separately and monitored separately," Ghinai said. "But even without that it is a variant of concern, it's being monitored very closely at the local levels, at the state levels and at the national levels."
How worried should you be about BA.2?
Ghinai said he believes the rise of BA.2 is "less concerning" than omicron was when it was first detected in the U.S. late last year.
"I don't expect the same kind of surge that we saw in late 2021 as a result of BA.2," he said. "That's not to say there won't be changes, especially at some point - we're at a nearly historic low in terms of COVID here in Chicago, it's very likely that there may be some changes in transmission. I don't expect it to be a surge like we saw the last few months because of omicron, because of delta."
That sentiment was echoed by incoming White House COVID-19 Response Coordinator Dr. Ashish Jha, who said he's watching what happens in the next couple weeks in the U.S.
"I'm not expecting a big surge here, but we're gonna have to pay close attention and really be driven by data as we have throughout the whole pandemic," Jha said last week.
U.S. health experts are warning BA.2 could soon lead to another uptick in domestic coronavirus cases.
White House chief medical advisor Dr. Anthony Fauci said BA.2 is about 50% to 60% more transmissible than omicron, but it does not appear to be more severe.
"It does have increased transmission capability," Fauci said Sunday on ABC's "This Week." "However, when you look at the cases, they do not appear to be any more severe and they do not appear to evade immune responses either from vaccines or prior infections."
Preliminary data indicate vaccinations and boosters are similarly effective in preventing symptomatic cases of BA.1, the original omicron variant, and BA.2.
"People are watching BA.2 very closely because it appears to have a growth advantage over BA.1," Ghinai said. "So to put that into, kind of, plain English, it means it's probably more transmissible than BA.1. But the difference between BA.1 and BA.2 is much, much smaller than the difference between omicron as a whole and delta as a whole."
According to Ghinai, evidence so far suggests infection with one omicron sublineage is believed to provide protection from other omicron sublineages.
"Obviously we're watching this closely, we're concerned about it, but I have been reassured in some, you know, really good real world studies that suggest, you know, about a 90% protection in at least the short term," CDPH Commissioner Dr. Allison Arwady said. "So, people who just recently, if they had, for example, a breakthrough infection from the original omicron, BA.1, it looks unlikely based on what we've seen in other setting that we would expect those same people to likely be particularly susceptible to BA.2."
Fauci said he expects "an uptick in cases" due to BA.2, but not necessarily a massive surge like other variants have caused. That's despite the Centers for Disease Control and Prevention recently relaxing mask recommendations for most Americans.
What's happening in Europe?
As most COVID-19 restrictions are relaxed across Europe, including Austria, Britain, Denmark, Germany and France, the numbers of infections have inched higher in recent days. The uptick is driven in part by the slightly more infectious omicron descendant BA.2 and by people largely abandoning masks and gathering in bigger groups.
In the last two weeks, COVID-19 hospitalizations and deaths have both risen slightly in Britain.
"I'm going to be honest, I am concerned about what's happening in Europe because I think there is not a full understanding of it," Arwady said during a Facebook Live Thursday.
Germany's disease control agency reported 294,931 new cases in 24 hours on Thursday.
Elsewhere, South Korea had its deadliest day yet of the pandemic on Tuesday, with 293 deaths reported in the latest 24 hours, as the country grapples with a record surge in coronavirus infections driven by the fast-moving omicron variant.
China banned most people from leaving a coronavirus-hit northeastern province and mobilized military reservists Monday as the fast-spreading “stealth omicron” variant fuels the country's biggest outbreak since the start of the pandemic two years ago.
Could Europe's rise in cases be a signal of what's to come for the U.S.?
"I think it's very likely that what we've seen in Europe, where BA.2 is increasing in relative proportion, is going to happen here," Ghinai said. "We're going to see BA.2 causing an increase in proportion of the number of cases. We've already seen that."
According to data estimates from the Centers for Disease Control and Prevention, the variant represented 23.1% of cases from March 6 through March 12. That's up from 13.7% earlier this month.
Across much of the Midwest, however, the variant accounts for 20.5% of cases during that same time frame. In parts of the East Coast, including New York and New Jersey, the number is 39%.
Arwady stressed that while the rise of COVID in other countries could be a sign of what's to come, it's not a guarantee.
"It is not a for sure thing, to be clear, that we will follow. We may, but there are some other countries that have gone through an omicron surge and we've not seen that resurgence yet," she said. "So we're still watching."
Arwady said that while her office has been in communication with the UK, the rising metrics could be due to any combination of restrictions lifting, waning immunity or BA.2 and other variants.
She noted that many countries currently seeing spikes, such as China and Australia, "were really aiming for a zero-COVID approach."
"What I think we've seen with omicron - BA.1, BA.2, doesn't matter - it is so much more infectious, so much more contagious, that countries that had been aiming for a zero goal, it's really not possible with a variant that infectious. And so what's important is that a lot of these countries, while they're seeing surges in cases, it's not turning into the, you know, sort of the severe illness, the hospitalizations because they're highly vaccinated. My worry is we are not as highly vaccinated as a lot of those other countries."
Is BA.2 in Illinois?
Stealth omicron had already been detected in Illinois earlier this year.
Northwestern Medicine's Center for Pathogen Genomics and Microbial Evolution said the subvariant was found in a Chicago resident who was tested for COVID-19 on Jan. 18.
According to data from the Centers for Disease Control and Prevention, variant surveillance measures in the Midwest indicate BA.2 cases are doubling every seven days.
What else should you know?
Based on how quickly new variants have arisen, some experts suggest the next one could arrive as early as May.
Ghinai said public health officials are "certainly expecting more variants to emerge," but it remains unclear if such variants will be more or less severe than previous strains.
"There's actually no strong scientific reason to believe that as the virus evolves it's going to become less and less severe," he said.
The biggest indicator of how severe a new variant could be, according to Ghinai, comes from immunity and vaccination.
"Whether or not they become less severe, I think, is actually mainly dependent on us," he said. "And I think the biggest thing that made omicron less severe than previous waves, I think the biggest difference was in people being vaccinated, or people having had prior infection and being somewhat immune as a result of that."