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The Delta Variant Is Extremely Contagious, But CDC Says Vaccines And Masks Will Help

SCOTT SIMON, HOST:

July began with a sense of relief in the U.S. It ends with a flurry of new mandates and reminders of just how dangerous the coronavirus can be. New data released by the Centers for Disease Control and Prevention point to why the agency changed its guidance, now recommends even fully vaccinated people mask up indoors in places where the virus is spreading. But we stress vaccination is still the best way to protect yourself from getting sick. The delta variant is responsible, and that more contagious version of the coronavirus is a warning flag to researchers.

Here to talk us through all of this is NPR health correspondent Maria Godoy. Thanks so much for being with us.

MARIA GODOY, BYLINE: My pleasure.

SIMON: Please tell us what we know today that we just didn't know last week.

GODOY: Well, we knew that the delta variant was more than twice as contagious as the original strain. What we've learned this week is that it's so contagious, when a fully vaccinated person gets a breakthrough infection, the levels of virus found in their nose is just as high as someone who hasn't been vaccinated, meaning they can transmit and spread the virus. That's a big deal, and it's why the CDC is now advising the vaccinated to mask up indoors in public places.

We learned yesterday that a lot of this information comes from an outbreak on Cape Cod. Starting with the July 4 celebrations and for the next couple of weeks, several hundred people, most of whom were vaccinated, got infected at large public gatherings. And what this tells us is that breakthrough cases are contributing to the spread.

SIMON: Does this mean the vaccines are losing effectiveness?

GODOY: Well, so the good news is that vaccines are still extremely effective when it comes to protecting people against severe disease and death, even in the face of delta. The bad news is that if you're unvaccinated, it's looking like the delta variant may potentially make you sicker. That's according to an internal CDC slideshow that was leaked Thursday night, and it pointed to studies from Scotland, Canada and Singapore showing people infected with the delta strain may be three to four times more likely to end up in the hospital and twice as likely to die compared with previous strains.

SIMON: And please tell us about the dangers as the virus continues to mutate.

GODOY: So delta is still the most concerning strain here in the U.S., but the virus is constantly adapting. That's what viruses do. They evolve. I spoke with Stephen Goldstein. He studies virus evolution at the University of Utah. He calls delta a warning.

STEPHEN GOLDSTEIN: It is a warning for us that there are - can be variants that arise. There's no rule that says delta has to be as bad as it can get. And over time, we are going to get variants emerge that are less - even less susceptible to the vaccines.

SIMON: Less and less susceptible to the vaccines - how likely is that to happen?

GODOY: Well, this week, European researchers released a new modeling study that asked that question. They wanted to know what factors might raise the risk that a vaccine-resistant strain emerges. And one of the surprising things they found is that the risk is highest when you have a lot of the population vaccinated, but you also have a lot of transmission going on, like we do now. The model finds that's exactly the wrong time to ease up on mask-wearing and other precautions. And the reason why is that the more people you have infected, the more opportunity the virus has to mutate into something vaccine resistant. And if you had a vaccine-resistant strain emerge when there's a lot of vaccinated people around, it would have an evolutionary advantage over other strains. The model suggests when there's lots of transmission, you want to keep masking and take other precautions to prevent spread until almost everyone is vaccinated so that the virus doesn't get the chance to evolve into something worse.

SIMON: That's a grim thought, Maria.

GODOY: Yeah, but the way to avoid that scenario is to vaccinate everyone and do it quickly. Every researcher I've spoken with says that's ultimately the way out of this.

SIMON: NPR health correspondent Maria Godoy, thanks so much.

GODOY: My pleasure. Transcript provided by NPR, Copyright NPR.