As the omicron surge continues to decline in the U.S., infectious disease experts are keeping a close eye on an even more contagious version of the variant that could once again foil the nation's hopes of getting back to normal.
The virus, known as BA.2, is a strain of the highly contagious omicron variant that appears to spread even more easily — about 30% more easily.
Because BA.2 quickly overtook the original omicron in South Africa and other countries and has even caused a second omicron surge in Denmark, researchers have been bracing for the same thing to happen in the U.S.
"A lot of us were assuming that it was going to quickly take off in the United States just like it was doing in Europe and become the new dominant variant," says Nathan Grubaugh, an associate professor of epidemiology at the Yale School of Public Health.
So far that hasn't happened. Instead, BA.2 has slowly, but steadily spread even as the omicron surge continued to dissipate. The fear is that spread may be on track to rapidly accelerate in the near future.
BA.2 has now been found from coast to coast and accounts for an estimated 3.9% all new infections nationally, according to the federal Centers for Disease Control and Prevention. It appears to be doubling fast.
"If it doubles again to 8%, that means we're into the exponential growth phase and we may be staring at another wave of COVID-19 coming in the U.S.," says Samuel Scarpino, the manager director of pathogen surveillance at the Rockefeller Foundation.
"And that's of course the one we're really worried about. We're all on the edge of our seats," he says.
Some experts think it's unlikely BA.2 will trigger a massive new surge because so many people have immunity from prior infections and vaccination at this point.
"The most likely thing that's going to happen is that it might extend our tail, meaning it might slow down the decrease in cases. But it's probably not going to lead to a new wave of cases," says Grubaugh.
Omicron is still infecting more than 100,000 people and killing about 2,000 people every day in the U.S. So even though BA.2 doesn't appear to make people sicker than the original omicron, just slowing down the decline in new cases would translate to more serious illness and death.
And adding to the concern, one of the remaining antibody treatments for COVID-19 may be less effective against BA.2, according to recent research.
"There are going to be plenty of people getting sick and ending up on respirators and dying because of BA.2," says Dr. Jeremy Luban, a virologist at the University of Massachusetts Medical School, especially among the millions who still aren't vaccinated.
Although vaccination and prior infection does appear to protect people against BA.2, this version of the virus seems somewhat better at evading the immune system than the original omicron was. This increases the concern that it could drive a growth in new cases.
And while Luban agrees the most likely scenario is that BA.2 will just extend the omicron wave, he says it's impossible to rule out the possibility of another surge.
"It may be that the virus has to get to somewhere like 5-7%, and then all of a sudden once it has a foothold like that, it will take off," Luban says.
Especially if that happens just as mask mandates and other restrictions are being lifted across the country and people are really letting down their guard.
"There is this lurking threat of BA.2. And we need to make sure this isn't going to be a problem before we roll back all the mandates, before we tell everybody that it's safe," Scarpino says.
Otherwise, the nation could get blindsided yet again.
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