More contagious than other variants, and maybe more likely to cause severe disease, Delta is spreading so fast in the U.S. it could cause another surge this summer or fall, according to new research.



The delta variant of the coronavirus was first identified in India. Now it's spreading in the U.S. so quickly that it will probably become the dominant strain of the virus within a few weeks. NPR health correspondent Rob Stein has been looking into some new research that makes this claim. Good morning, Rob.

ROB STEIN, BYLINE: Good morning, Noel.

KING: Who's doing this research, and what did they find about the delta variant?

STEIN: This comes from a testing company called Helix that's helping the CDC track the variants. Researchers analyzed more than 243,000 samples of the virus collected across the country over the last six months or so, and they found that two variants really started to take off around the beginning of May. One is called - the so-called gamma variant. It was first spotted in Brazil. And the other is this delta variant. According to this analysis, the gamma variant now accounts for 16% of infections, and delta now accounts for at least 14%. But delta appears to be spreading two or three times as fast as gamma, and so it looks like it's outcompeting all the other variants in the country at the moment.

KING: OK. And what are the implications of that?

STEIN: So it appears that the delta variant is so contagious and on such a fast trajectory that it could become the dominant virus in the U.S. within three or four weeks, basically taking over, like it did in the U.K. and so many other countries. I talked about this with William Lee. He's the VP of science at Helix.

WILLIAM LEE: It definitely is of concern, and it's a concern because it's highly transmissible. Right? Just the fact that it is so transmissible means that it's dangerous.

STEIN: And it could trigger new outbreaks around the country.

KING: Do the vaccines that millions of us have been getting work against the delta variant?



STEIN: The vaccines look like they do work really well against the delta variant, but that's only if people are fully vaccinated. Partially vaccinated people are still vulnerable, and unvaccinated people are totally unprotected. I talked about this with Dr. Jeremy Luban at the University of Massachusetts Medical School.

JEREMY LUBAN: There still are big portions of the country where the rates of vaccination are quite low. And, in fact, the Helix paper shows that this delta variant is increasing in frequency. The speed at which it's increasing in frequency is greatest in those areas where vaccination rates are lowest.

STEIN: Like a bunch of Southern and, you know, Western states.

KING: So we've had these waves and surges over the past year. Could the delta variant cause another surge?

STEIN: You know, Noel, it very well might. A new set of projections are just out from a group called the COVID-19 Scenario Modeling Hub. It's helping the CDC figure out where the pandemic might be going. And it concludes that a highly contagious variant, like delta, could trigger yet another wave as soon as sometime in July and continuing at least into November. Justin Lessler is an epidemiologist at Johns Hopkins who's been helping coordinate the modeling hub.

JUSTIN LESSLER: For the most part, it's a moderate resurgence. I think I'd characterize it as sort of a continuation of the doldrums. We're not having massive epidemics at a national level, but we have this kind of continuation of the virus just sticking around and keeping us on our toes.

STEIN: You know, especially in those places where a lot of people aren't vaccinated. And the situation could get even worse later in the fall and winter, you know, when people start spending more time indoors again.

KING: Sure. NPR health correspondent Rob Stein. Thank you, Rob.

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