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caption: A computer generated image of the omicron variant. 
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A computer generated image of the omicron variant.
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A second version of omicron is spreading. Here's why scientists are on alert

Just as the omicron surge starts to recede in parts of the U.S., scientists have their eye on another variant, spreading rapidly in parts of Asia and Europe.

It's officially called "omicron BA.2," and this week scientists detected cases of it in several states, including California, Texas and Washington.

Although BA.2 is currently rare in the U.S., scientists expect it to spread here over the next month. There's growing evidence that it's just as contagious as – or possibly a bit more contagious than – the first omicron variant, called "omicron BA.1."

"It could be that BA.2 does have some small advantage," says Emma Hodcroft, who's an epidemiologist at the University of Bern and has been tracking variants all around the world via the Nextstrain project throughout the pandemic. "BA.2 might well be like, 1% to 3% more transmissible, or something like that."

So the big question now is: Will that small difference be enough for this variant to lengthen the ongoing surge in the U.S. as it has in Denmark.

What is Omicron BA.2?

You can think of a BA.2 as a sibling to BA.1, Hodcroft says. They share a bunch of mutations – about 30 or so – but they also have a bunch of mutations that are unique.

"They are quite similar, but they're also different, " she says. "So very much like siblings, in my opinion. Different but obviously related."

Back in November, when scientists in South Africa and Botswana first discovered omicron, they didn't find just one version. They found three, called BA.1, BA.2 and BA.3 by the Phylogenetic Assignment of Named Global Outbreak Lineages at the University of Edinburgh.

The first one, BA.1, took off rapidly and spread around the world, including in the U.S. And initially, it looked like BA.2 and BA.3 were weaker and less able to keep up with BA.1.

"We thought, 'OK, BA.2 is just not as fit as its sibling, BA.1,' and it will kind of peter out," Hodcroft says.

But that's not what happened – not at all.

Is omicron BA.2 as transmissible as omicron BA.1?

Over the past several weeks, omicron BA.2 has begun to surprise scientists. And it's starting to look like it can, in some countries, outcompete its sibling, omicron BA.1 – and really any other variants.

Back in December, omicron BA.1 caused a massive surge in cases in Denmark, similar to the surge in the U.S. But then, just as cases began to decline, BA.2 started spreading very rapidly in Denmark. After only a few weeks, BA.2 took over the outbreak there and has lengthened Denmark's surge. Denmark's cases are climbing steeply, with more than 40,000 recorded each day. Since the second week in January, BA.2 has caused more than 50% of those cases, according to the Statens Serum Institut in Copenhagen.

Omicron BA.2 is also growing exponentially in England and Germany, where it's causing at least 5% of cases in both locations. Scientists are concerned it could lengthen surges in those countries as well as possibly in the U.S.

Together, this data indicates that BA.2 is not BA.1's weaker sibling, but rather that BA.2 is quite strong and possibly more contagious.

Is BA.2 more dangerous than BA.1?

Many studies have shown that infections with omicron BA.1 carry a reduced risk of severe disease compared to the delta variant.

Preliminary evidence from Denmark suggests this will also be the case with omicron BA.2, says Dr. Peter Chin-Hong at the University of California, San Francisco.

"Scientists there have found that there was no increased risk in going to the hospital if you have BA.2 compared to if you have BA.1," Chin-Hong says. "That could change but that's what we know so far."

And there's cautious optimism about inoculations. Preliminary data from the U.K. government shows that a third shot of the vaccine protects against an infection of BA.2 just as well as it does against BA.1. In both cases, it reduces the risk of a symptomatic infection by about 60 to 70%. In addition, there are many similarities in BA.1's and BA.2's spike proteins – the part of the virus that many antibodies target.

So Chin-Hong expects the vaccines will likely provide superb protection against severe disease.

"I have no guarantee that you won't get infected or possibly reinfected [if you've already had Covid], meaning that you might have the sniffles or feel like you have another cold, but I feel very, very confident that you would be protected from serious disease in the general population."

And Chin-Hong says, this distinction is critical for the future of Covid. Going forward, he says, communities need to shift their focus from stopping all infections to keeping everyone safe from severe disease and hospitalization. [Copyright 2022 NPR]