People wonder if they should keep calm and carry on in the face of delta plus variant

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Lockdowns have been eased in the United Kingdom, but now there's a new variant called delta plus emerging. Will it take off the way delta did? / Getty Images

Oh no. Not again.

Just when COVID surge in the U.S. has begun to decline, another coronavirus variant has immediately cropped up. This time in the U.K.

Known in the media as "delta-plus," this mutant is raising some concern because over the past few weeks, it's begun to spread in several parts of Britain. It now accounts for about 6% of all cases in the U.K.

To find out what's going on with this new variant — and the risk it could swoop into the U.S. and cause another resurgence — NPR spoke with three people who have been following the variants like hawks since the first ones emerged last fall.

Question 1: The name of the variant is a bit scary, delta-plus. If delta is already highly contagious, what does the "plus" mean?

"It's a bit like delta's grandchild," says epidemiologist William Hanage at Harvard University.

After delta was first identified last year in India, it continued to evolve and pick up more mutations. And these mutations have created many variants of delta, including ones here in the U.S.

All these new versions are descendants of delta, Hanage says. "Delta-plus has been used interchangeably for any descendant of delta that people are getting their knickers in a twist about now. Whether they should or should not be getting their knickers in a twist is another question."

In the past, Hanage points out, all of these previous delta-plus mutants have turned out not to be much different than the original delta. They aren't more dangerous or more transmissible.

Question 2: So what about this new "delta plus" that's spreading in the U.K.? Scientists have named it "AY.4.2." And it now accounts for more than 6% of the cases there. Does that mean it's more transmissible than the current version of Delta dominating in the U.S.?

"No one knows yet," says virologist Jeremy Luban at the University of Massachusetts Medical School. "It's too early to really know."

That's because there isn't enough data yet to measure its transmissibility. "That said," Luban adds, "if it is more transmissible, it's likely to be a small increment."

Hanage estimates that it's likely about 10% more transmissible than the original version of delta.

Remember, delta is already super contagious. So adding 10% more likely won't change the behavior of the variant dramatically. (For instance, say you have a supercharged engine on your truck, if you bump up the turbocharge by 10% more, it's not that much more supercharged.)

Question 3: But that's still some increase in transmissibility. Could delta-plus sweep across the U.S. and reverse the lull in cases here the way the regular delta did this past summer?

"There's no obvious sign that it's going to take off the way that delta did," Luban says. "I think if you polled people who are following these variants, most of them would tell you that 'AY.4.2 is unlikely to be a new delta. It's unlikely to totally just take over. It's more likely to be a slow, creeping increase in cases."

Epidemiologist Justin Lessler of the University of North Carolina has even used computer models to see what might happen when new variants come to the U.S. He and his colleagues ran a simulation with a variant that's 50% more transmissible than delta and then looked to see what happened.

"Even with a variant that's way more transmissible than delta-plus, cases didn't go back to the types of peaks we saw last winter or even the types of peaks we've seen in the delta wave," Lessler says.

Right now, in the U.S. many people have some protection from SARS-CoV2 because they've built up immunity through infections, vaccinations or both, he says. To reverse the lull in the U.S., he says, it will likely take a variant with more than increased transmissibility.

For example, if a variant emerges that can escape detection by antibodies, then we could potentially see a big resurgence, Lessler adds. So far, there's no evidence that the delta-plus has this ability.

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