KELSEY SNELL, HOST:
Health officials around the world are adjusting their plans for combating the coronavirus pandemic in light of the more infectious delta variant and concern that even vaccinated people can spread it. Here in the United States, for example, the Centers for Disease Control and Prevention is once again recommending that everyone, including those who are vaccinated, wear masks indoors in high-risk areas. We wondered why the delta variant is causing problems that other variants haven't. So we asked NPR science correspondent Joe Palca to help explain that. Hi, Joe.
JOE PALCA, BYLINE: Hi, Kelsey.
SNELL: So what is it about the delta variant that's causing all of these problems? How are people who are vaccinated supposed to think about this?
PALCA: Well, the first thing they should know is that the vaccines work. And what they're supposed to do is prevent you from getting extremely sick or winding up in the hospital or dying. So that's the first thing. Keep that in mind. But vaccines give you systemic immunity, meaning all the inner organs of your body, like the lung and the kidney and the liver, are protected. But it doesn't give you local immunity. That is, in the nose and throat, and that's where the virus gets in. Now, it turns out the delta variant is particularly good at replicating in the nose and throat so it can take hold there even if a vaccinated - even though a vaccinated person will be protected from serious disease.
SNELL: So what you're saying is the current vaccines, the ones that people are getting right now, are not really designed to prevent the coronavirus from infecting the nose and throat?
PALCA: Not specifically. But I talked with Frances Lund, who's chair of the department of microbiology at the University of Birmingham in Alabama (ph), about that. And she says, if you have a really - I'm sorry. It's the University of Alabama in Birmingham. And she says if you have a really strong immune response after getting vaccinated, then you might be protected in both the lungs and the upper airway, such as the nose and throat from infection. On the other hand...
FRANCES LUND: If your vaccine response is not super-duper or it's starting to wane a little bit and you have a virus that could replicate really fast, then, yeah, you will end up with some limited period of time where that virus is replicating even in the vaccinated people.
PALCA: So if you were to take a nasal swab from that person, then, yes, they'd be infected. But the key is that for someone who is vaccinated, the virus might not be able to main (ph) its foothold in someone's nose, if you'll forgive the mangled metaphor.
LUND: In other words, they might be infectious for a day or two. Somebody who's not vaccinated - it'll be a week or more that they could be transmitting the virus.
SNELL: So what determines whether someone who does have the virus in their nose will transmit it to other people? Do we know?
PALCA: Well, not specifically. But it's this idea that every time you cough or sneeze or even if you're breathing heavily and you happen to be standing near someone - the more viruses there is in the nose, the more likely the sneezes and coughs will contain virus particles that could infect someone.
SNELL: And what does this mean about, you know, in terms of those breakthrough infections among vaccinated people that we're hearing so much about right now?
PALCA: Well, the delta variant may be slightly, slightly more likely to cause a breakthrough infection. That's not certain. But since it's spreading now and since it's the main virus out there, if you're going to have any kind of breakthrough infection, it's going to be with the delta variant.
SNELL: So since we know all of this, is anybody working on a vaccine that would block the virus from infecting those cells in the nose and throat in the first place?
PALCA: Yes, these are vaccines that are administered by - as a nasal spray. And they have something like that for the flu vaccine. Frances Lund says there are seven different COVID-19 vaccines being studied in human subjects. And it's early days for those studies. And it's not clear whether any of them work because creating nasal vaccines against the coronavirus virus is something researchers are just learning to do.
LUND: We know how to do it in a mouse, but that does not mean we know how to do it in a human.
SNELL: So seven different vaccine candidates being studied. That's a lot. But that, like you said, can take a while. What can people do if they don't want to transmit the virus to others while they're waiting?
PALCA: Well, they could lock themselves in a closet and not interact with anybody.
PALCA: But that's probably the bad plan. A much better plan is to wear a mask. That's what health officials have been saying. A lot of the time, you don't know when you're sick. That's the devious thing about this virus. But you can still be infectious. So a mask is the safest thing to do when you're in a place where you could possibly infect other people.
SNELL: That was NPR science correspondent Joe Palca. Joe, thanks for joining us.
PALCA: You're welcome.
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