1 big reason experts believe the US will not suffer the next COVID wave as badly as Europe

• A more transmissible version of Omicron, named BA.2, has been sweeping Europe.
• Because of the way variants have traveled across the Atlantic in the past, there's some concern BA.2 is going to hit the US hard next.

Omicron is changing its shape again. Another Omicron subvariant, BA.2, is quickly displacing its relatives in the US.

It is more contagious than its viral peers and predecessors, causing swift damage in Europe and Asia — traveling and infecting at a clip people haven't seen yet. Naturally, that is stoking fears that BA.2 could trigger a new surge in cases in the US. As of publication, BA.2 was already responsible for about a third of cases in the US, and the majority of all cases globally.

But there's reason to think that BA.2's story may play out quite differently in the US than it has in other places.

That's due to a confluence of factors, chief among them the level of hodgepodge immunity to Omicron in the US already, from vaccines, boosters, and earlier infections. All of that, taken together, suggests that BA.2 in the US might behave more quietly, as it did in South Africa.

BA.2 is more transmissible than other Omicrons, and is already sweeping the US

Experts estimate BA.2 is roughly 30-50% more transmissible than the "original" Omicron. For instance, the UK government is reporting that BA.2 has a secondary attack rate of more than 13% among household contacts. (The household attack rate was previously around 10% for other Omicrons.)

"We likely will see an uptick in cases," President Joe Biden's chief medical adviser, Dr. Anthony Fauci, said on ABC's This Week on Sunday, but he added, "hopefully, we won't see a surge. I don't think we will."

Harvard epidemiologist Bill Hanage predicted on Andy Slavitt's "In the Bubble" podcast on Monday that the US will see a new wave, and some areas will be hit harder than others.

But, Hanage added: "I don't think it's going to be as dramatic as Europe, because the recent pandemic history has been really quite different, and because most of Europe has been pretty COVID-averse, you know. Whereas parts of the United States have been quite COVID-curious."

Europe suddenly dropped mask mandates — and exposed a COVID-naive population to the new variant

The Institute for Health Metrics and Evaluation, one of the premier disease modeling centers in the US, said in a briefing document "the most important explanation" for Europe being hit hard by BA.2 is that the variant emerged just as people took off their masks and returned to offices and indoor events.

The virus suddenly had a fresh opportunity to infect a lot more people than it did previously in Europe, and given its higher transmissibility, BA.2 quickly found many new people to infect.

In the US, many people have been going maskless and mingling with strangers for far longer — already, it's estimated that around 40% of the country has had an Omicron infection. That exposure wasn't without consequences. Nearly a million US cases of COVID-19 have been fatal so far, equating to the third highest recorded death toll from COVID-19 in the world, per capita. During the peak of the Omicron wave, in late January and early February, more than 3,000 people were dying from the virus in the US each day.

But despite the painful, deadly way it came about, the immunity the US has today is important because there are good indications that a previous Omicron infection — even from a different version of it — does cross-protect most people from BA.2.

More than three-quarters of the US has had some kind of COVID-19 infection at some point during the pandemic, compared to about 55% of the UK, and each survived exposure helps inform the immune system (even if vaccination is by far the safest way to teach it how to fight.)

"The more times we have encountered the spike protein, the more robust our immune response, when it comes to preventing a severe infection, even with a variant which is as wild as Omicron," Hanage said.

Evidence suggests vaccinated people who got Omicron in the first wave will be protected

According to data on a very small group of a few dozen patients, published in the New England Journal of Medicine on March 16, there is decent cross-protection from BA.1 to BA.2 infections.

That means that people who've been vaccinated, boosted, and exposed to Omicron may not be very susceptible to getting infected with BA.2, at least for now.

Omicron reinfections do happen, of course, but they are exceedingly rare in people who've had Omicron before. And fortunately, for now, hospitalization rates with BA.2 don't appear any worse than they were for other Omicron subvariants.

Looking to the Northeast for clues about what BA.2 will do next

The US's Omicron immunity will, inevitably, wane. And it's not clear how soon that'll happen, or how strong the current immunity really is. That's keeping immunologists very cautious with their predictions.

"We don't know what BA.2 will look like in the US," infectious disease expert Katelyn Jetelina said in her newsletter on Monday. "BA.2 is finishing BA.1's job," she said, which is "making overall global patterns inconsistent."

One possibility that both Jetelina and the IHME think is possible is that BA.2 could prompt a short spike in cases, at least in some areas of the country, but maybe not in others. Jetelina points out that the Northeast currently has the greatest prevalence of BA.2 anywhere in the country, so that may be a good place to look to in forecasting any forthcoming uptick.

For now, the sewers of the Northeast aren't suggesting much of a spike on the horizon. Boston, which has one of the most useful COVID wastewater dashboards in the country, is not seeing any major increase in COVID-19 in the wastewater just yet:

But it's worth keeping an eye on wastewater COVID-19 levels, in cities like New Haven and New York too, as they could be beacons for any impending US surge.

As Denmark has so painfully seen, just because BA.2 is no more severe than its predecessors doesn't mean it can't be deadly for vulnerable people, like older adults, especially those that don't yet have boosters.

"Even if we dont have a big BA.2 wave overall, we may still see a surge in risk for high-risk groups," epidemiologist Ellie Murray from Boston University said on Twitter.

One thing all the experts can agree on is that it's better to be on alert for whatever the virus might hurl our way next, and ready our defenses.

"This virus has a habit of flipping the script" Hanage said. "Be prepared for what you're going to do if it does."