CDC Says More Virulent British Strain Of Coronavirus Now Dominant In U.S.

Apr 7, 2021
Originally published on April 7, 2021 10:17 pm

A more easily spread coronavirus variant first identified in England last year has now become the dominant strain in the U.S., the head of the Centers for Disease Control and Prevention said Wednesday.

The variant, known as B.1.1.7, spread quickly across the United Kingdom and Ireland beginning last fall, with the more infectious version of the coronavirus thwarting restrictions and lockdowns that had earlier helped keep the original strain in check.

B.1.1.7 is "now the most common lineage circulating in the United States," CDC Director Rochelle Walensky said at a White House media briefing on Wednesday.

The announcement comes as the number of cases — particularly among younger Americans — has been on the rise in the U.S., fueling fears that the nation may be facing yet another deadly surge.

Walensky said that the newer strain has been shown to be more transmissible among younger people and that new outbreaks in the U.S. have been linked to youth sports and day care centers.

She urged people not to let their guard down and to get vaccinated as soon as possible. She said that communities and states with high levels of transmission need to curtail or suspend sports activities for younger participants to contain the spread of the new strain. She also said large events in affected communities needed to be curtailed.

"The virus still has a hold on us," she said. "We need to remain vigilant."

The CDC warned in January that B.1.1.7 would likely become the dominant strain of SARS-CoV-2 — the coronavirus that causes the disease COVID-19 — in the U.S. by the end of March.

Based on evidence gathered in the U.K., "it was predicted that this SARS-CoV-2 variant would dominate the USA within a matter of weeks. The prediction was indeed correct, and confirms that the work done in the UK was excellent," Jeremy Luban, a biochemist at the University of Massachusetts Medical School, said in an email to NPR.

Studies have suggested that the variant is about 50% more transmissible than the strain of the coronavirus first identified in China in December 2019.

Luban said that this could explain the sudden increase in cases in the United States.

"That being said, the more likely problem is that many states have opened up restaurants and other public indoor spaces, places where transmission rates are highest," he said.

The fact that the B.1.1.7 strain is more easily spread gives it the potential to kill more people.

"If you then crank that exponential growth up to a steeper curve, you very quickly start infecting many, many, many more people than you would have beforehand," epidemiologist Emma Hodcroft at the University of Bern in Switzerland said in January.

There is also evidence that this variant makes people sicker, says William Hanage, a professor of epidemiology at Harvard University.

Hanage said it was "inevitable" that the B.1.1.7 variant would become the dominant strain in the U.S. but expressed some optimism about the timing.

"[A]t least this is happening at a point when we have a decent amount of vaccination even if it is nowhere near enough to control B.1.1.7 on its own," he wrote in an email to NPR.

Hanage said two factors were driving down the mean age of hospitalizations in the U.S.: "the first is that older adults are vaccinated and so less likely to wind up in hospital."

The second factor, he said, "is that the younger age groups now being infected with B.1.1.7 are more likely to have severe disease, because the variant is more virulent."

The U.S. leads the world with nearly 31 million confirmed coronavirus cases since the start of the pandemic, with 556,000 deaths due to COVID-19.

Copyright 2021 NPR. To see more, visit


The more contagious coronavirus variant first spotted in the U.K. is now dominant in the United States. That is the worrisome news today from the Centers for Disease Control and Prevention. NPR health correspondent Rob Stein is here with the details.

Hey, Rob.

ROB STEIN, BYLINE: Hey there, Ari.

SHAPIRO: So CDC director Rochelle Walensky shared this information at today's White House COVID briefing. Tell us more about what she said.

STEIN: Yeah. So Ari, you know, this is something that the CDC and others have been worrying would happen and in fact predicted would happen for a while now - that a mutant strain originally spotted in the U.K. - it's officially known as the B.1.1.7 variant - would become the dominant virus spreading around the U.S. And Walensky said that fear has come true.


ROCHELLE WALENSKY: Based on our most recent estimates from CDC surveillance, the B.1.1.7 variant is now the most common lineage circulating in the United States.

STEIN: Basically, it's everywhere, and it's spreading fast.

SHAPIRO: Remind us why this particular variant is so concerning.

STEIN: So first of all, this variant is way easier to catch, so it spreads faster, which makes everything, you know, everyone's been doing to protect themselves way harder. You know, staying away from other people, wearing masks, washing our hands still all work, but people really have to kind of double down on all that to slow down this version of the virus.

And the dominance of this variant is probably one of the reasons why infections have started rising again in the U.S. and why the country could be facing, you know, yet another surge in cases. It's not the only reason, but instead of doubling down on precautions, people are doing the opposite. They're traveling more, crowding into bars and restaurants, baseball stadiums, states are easing up. And second of all, it looks like this variant tends to make people sicker, which may help explain why we're seeing more younger people get really sick now. So the U.S. could see deaths start rising, too.

SHAPIRO: And I guess the big question is how well the vaccines work against this variant.

STEIN: Yeah. So there's some good news. So far, the evidence is yes, the vaccines seem to work. You know, if you look at other countries like Israel, vaccination campaigns tame the pandemic even though the B.1.1.7 variant was dominant. So that is good news.

But as everyone keeps saying, the country is in this race to vaccinate as many people as fast as possible to try to protect them from catching this and, you know, possibly getting really sick and even dying before they can get vaccinated. And the big fear is the more the virus spreads, the greater the chance it or other versions of the virus could mutate more in some way that could help it evade the vaccines.

SHAPIRO: And this is not the only variant circulating. What can you tell us about the others?

STEIN: Yeah, yeah, yeah, that's right. There are more contagious homegrown variants, too, like a couple first spotted in California that are now dominant out west. There's one originally spotted in New York City that is now becoming dominant in lots of other places in the northeast.

And there are a couple others first identified overseas. There's that one that was first spotted in South Africa that's really worrisome because it - not only does it spread faster, but the vaccines may not work as well against it. And it's been spotted in at least 36 states. And one first spotted in Brazil that looks like it may also be able to evade the immune system, it's been spotted in 25 states at least, including a big cluster on Cape Cod in Massachusetts.

So there may be others. And the big concern is that the U.S. still doesn't really do a really good job of tracking variants closely or spotting new mutants that may evolve.

SHAPIRO: NPR health correspondent Rob Stein, thank you.

STEIN: You bet, Ari. Transcript provided by NPR, Copyright NPR.