With COVID outbreaks being reported in a number of countries around the world and upticks being seen across Europe, many coinciding with a rise in BA.2 or "stealth omicron" cases, how worried should you be?
Three top Boston doctors said this week it remains unclear what effect the BA.2 subvariant will have on the city's fight against COVID, though they are keeping a close eye on what is happening in other parts of the world.
Here's what we know so far about BA.2:
What's happening in Europe and China?
As most COVID-19 restrictions are relaxed across Europe, including Austria, Britain, Denmark, Germany and France, the numbers of infections have inched higher there in recent days as well. 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.
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 that be a signal of what's to come for the U.S.?
Dr. Daniel Kuritzkes, Brigham and Women's Hospital's chief of infectious disease, said the surge in China is a stark reminder that the pandemic happens in waves.
"This is further evidence that the pandemic is not synchronous. It doesn't happen all together at the same time in all countries across the world," he said. "What we are seeing is this wave of omicron finally making its way into Asia, which had been relatively closed off to travel and commerce previously."
Boston Medical Center's Dr. Sabrina Assoumou agreed with her colleague. She said officials should use this surge in China to prepare here at home.
"This is a time where we should prepare and make sure we get as many people vaccinated as possible to prevent another surge here," she said.
Dr. Shira Doron, a hospital epidemiologist at Tufts Medical Center, said that while that number of cases may seem low, China has a different approach than other countries.
"What [China] calls a surge is a number of cases that are way lower than what we tolerate," she said. "They are taking aggressive measures to curb an increased case number that we here do almost nothing about."
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.
Health officials are looking very closely at whether or not BA.2 needs to be classified separately and monitored separately. But even without that it is a variant of concern, and is 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?
Medical officials don't expect that the rise of BA.2 will result in a spike in cases similar to the omicron surge late last year into early 2022.
Preliminary data indicate vaccinations and boosters are similarly effective in preventing symptomatic cases of BA.1, the original omicron variant, and BA.2.
“We do not see an increase in severity with BA.2. However, with huge numbers of cases you will see an increase in hospitalizations, and we have seen this in country after country,” the World Health Organization's Dr. Maria Van Kerkhove said.
But it could result in some changes in transmission, and there could be serious economic impacts on the U.S. as well.
"If a new variant emerges out of the current surge, we'll certainly have impacts on travel and commerce with Asia as they cope with the consequences of the current surge," Kuritzkes said.
Doron echoed that statement. "They have a different approach. They really are trying to reach that zero COVID status, but that in it itself will affect supply chains and other things like that."
Is BA.2 in Massachusetts?
Health experts said as far back as February that stealth omicron was probably already in Massachusetts.
When asked at the time how likely it was that the new subvariant was in Massachusetts already, Doron said, "Pretty likely."
"What we've learned is that, variants that are seen in other parts of the country don't always take hold here, but they always get here to some extent," she said. "So I think that we will find out that we have BA.2 in Massachusetts any day now."
Later that same week, Massachusetts General Hospital said stealth omicron had been identified in the state.
The Centers for Disease Control and Prevention reported earlier this week that the BA.2 subvariant makes up nearly a quarter of all coronavirus variants now circulating in the U.S. And in states such as Connecticut, Maine, Massachusetts, New Hampshire, Vermont and Rhode Island, the subvariant now makes up about 38.6% of total cases.
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.
Health officials say they are certainly expecting more variants to emerge, but it remains unclear if such variants will be more or less severe than previous strains.
The biggest indicator of how severe a new variant could be comes from immunity and vaccination, experts agree.
"People seem to forget or not really understand that when you get vaccinated, you're less likely to be infected and because you're less likely to be infected, you're less likely to transmit," Assoumou said earlier this year.
"Even if you became infected, you will shed for shorter periods of time because you will you will have a more rapid clearance of the virus," added Kuritzkes. "That you're going to be infectious for a shorter period of time is a very important point, because that's how vaccination helps to contribute to the control of disease."