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The Science Behind How COVID-19 Vaccines Work


More than a million people here in the U.S. have now gotten both doses of the COVID-19 vaccine. A week or two after that second booster shot, both the Moderna and Pfizer vaccines are about 95% effective at preventing symptomatic disease.

ANGELA RASMUSSEN: Reducing symptomatic disease means that you have fewer people going to the hospital. You will have fewer people dying of COVID-19.


Angela Rasmussen is a virologist at Georgetown University, and she says the vaccines prevent symptoms. And that's really important, but there are still unknowns.

RASMUSSEN: We still don't know how well this protects against infection and transmission. And although it's likely that it does, until we know more about that, we should really err on the side of caution.

KELLY: Right. So even after you are fully vaccinated, she says the virus may still be able to enter your body and replicate, meaning you could still pass the virus to others. We should know more about that in a few months. In the meantime...

RASMUSSEN: Even if you've been vaccinated, you're probably going to have to continue to take the same precautions that you've been taking in terms of wearing masks and physically distancing and avoiding enclosed spaces and crowds and so forth.

SHAPIRO: So to be clear, she is saying keep masking, keep distancing even after you get both vaccine shots to keep unvaccinated people safe.

KELLY: But as more shots are distributed in the months to come, maybe everyone in your immediate family has both doses, what then?

RASMUSSEN: Then you probably can go back to life as normal somewhat, as long as you're doing that in a sequestered environment. So you could, say, go on a weekend ski trip with a group of people who've all been vaccinated. But you should not be going out, like, barhopping or hanging out in the community with large groups of other people who have not been vaccinated.

KELLY: The goal, Rasmussen says, is to reach herd immunity before we go back to life as we knew it.

SHAPIRO: Dr. Anthony Fauci has estimated that more than three-quarters of Americans may need to get their shots before we reach that point. And he says that might not happen until the fall in this country. Remember; this is a global pandemic.

RASMUSSEN: And by definition, that means it's affecting the entire world. So none of us are safe unless all of us are safe. And that means that ultimately, our goal needs to be achieving the herd immunity threshold globally rather than just here in the U.S.

KELLY: So even if you have gotten the shots, might not be the time to hop on a plane to that international destination wedding. Getting truly back to normal is going to take time.

RASMUSSEN: When people are thinking about how the vaccine's going to help, I think of it as sort of being at the bottom of a well and climbing slowly up the side of it and seeing that circle of light at the top getting bigger and bigger as we get closer and closer. But there's no elevator in the well. I'm not going to suddenly, you know, rocket to the top of it, and things are going to be over.

SHAPIRO: Until we are out of that well - and you've probably heard this advice before - keep distancing, stay at home if you can and don't forget to wear your mask.

(SOUNDBITE OF TORTOISE'S "TEN-DAY INTERVAL") Transcript provided by NPR, Copyright NPR.