Pfizer COVID-19 Seems Promising But What's Next? : Short Wave Interim results are in from a large trial of an experimental COVID-19 vaccine. Drug maker Pfizer, working with German company BioNTech, says its vaccine appears to be working really well — it was found to be more than 90 percent effective. Today on Short Wave, host Maddie Sofia talks to NPR science correspondent Joe Palca about what that efficacy number means, details of the study and what more information about the vaccine researchers are awaiting.

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The COVID-19 Vaccine Trial Results: What They Mean, What Comes Next

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You're listening to SHORT WAVE from NPR.

Hey, everybody. Maddie Sofia here with NPR science correspondent Joe Palca. Hey, Joe.

JOE PALCA, BYLINE: And hello, Maddie Sofia, host of SHORT WAVE.

SOFIA: (Laughter) Hey, Palca. So you're here because this week, there's been a big COVID-19 vaccine development.


AILSA CHANG: Pfizer and its partner BioNTech announced today some promising but preliminary results...

PETER O'DOWD: Is more than 90% effective, a milestone but not yet conclusive.

PALCA: That's right. And company executives were pretty darn excited.


WILLIAM GRUBER: I'm - tend to be an optimist. I've been in vaccine development for over 35 years. And this is extraordinary. And I think it speaks well not only for the potential of this vaccine but potentially other vaccines out there in development for COVID-19.

PALCA: That was William Gruber, senior vice president of Pfizer Vaccine Clinical Research and Development. And the vaccine appears to be working really well. It was found to be more than 90% effective. And it wasn't just Gruber who was excited. I've been speaking with scientists all week who say this is a really positive result, better than they dared to hope.

SOFIA: Yeah. And, I mean, I don't know about you, but since the news came out this week, a lot of people have reached out wondering about this vaccine, what this news means for a vaccine to be effective and, you know, kind of what to expect now.

PALCA: Yeah. Those are big, important questions. And the pandemic has obviously upended life all over the world. So having a vaccine will be a huge step in figuring out what the world will look like as we learn to live with this coronavirus.


SOFIA: So today on the show, we break down the latest vaccine development, what it means and what researchers still need to find out. This SHORT WAVE from NPR.


SOFIA: So Joe Palca, the news this week about the Pfizer-BioNTech experimental vaccine is, on its face, pretty good. Let's dive into some of the details about what it means.

PALCA: OK. Sure. So Pfizer recruited a bunch of people for this vaccine trial, nearly 44,000 people.


PALCA: About half got the placebo. It's just a shot of salt water, essentially, saline. And the other half got the vaccine, two shots spaced 21 days apart. And they compared the number of people who got sick with COVID in each group, the vaccine group and the placebo group.

SOFIA: Got it. When you - and when you say sick, like, what does that mean? How do they define sick?

PALCA: Well, there are a lot of ways to define it. And different studies of different vaccines have used different markers. But in this case, the volunteers had to have at least one symptom - like coughing or sore throat or something like that - and a confirmed infection with a PCR test to be counted as a case of COVID. And what they found was that the majority of the confirmed COVID cases were in people who got the placebo.


PALCA: So the vaccine seemed to be stopping people from getting sick. It's somewhere, as we said, about above 90% efficacy, which is really good because, I mean, scientists were hoping for something better than 50 or 60% maybe. And 90 is, like, off the charts.

SOFIA: Yeah. Yeah. So this efficacy number, 90%, it's looking at how good the vaccine is in preventing the disease in people who have likely been exposed to the coronavirus?

PALCA: Right. Right. Let's just back up a second and talk about how the study is designed.


PALCA: Getting tens of thousands of volunteers ensures that a lot of people, who have really different jobs and habits and lifestyles, at some point have an equal likelihood of being exposed to the virus. But (laughter) this is a kind of a conundrum...

SOFIA: Right.

PALCA: ...Because people have to be exposed if you're going to find out if the vaccine works. But, at least in this trial, the researchers don't want people going out and getting exposed on purpose because that would be ethically inappropriate.

SOFIA: Right.

PALCA: So the volunteers are encouraged to continue to take the steps that we all know you can take to avoid infection - wash your hands, stay away from crowds, wear a mask. Maintain social distance - six feet. But some people will inevitably be exposed to the virus because of decisions they make or because of their jobs.

SOFIA: Got it.

PALCA: And a large number means that in each group, placebo or vaccine, there will be enough randomly exposed.

SOFIA: Yeah. And, I mean, unfortunately, with case counts exploding in the U.S., that's almost everywhere right now, you know? Like, you're almost guaranteed exposures in the U.S.

PALCA: Yeah. It's kind of dark, but it's accurate. And I should point out here that it's going to be a guaranteed exposure for both groups...

SOFIA: Right.

PALCA: ...Because this is what's called a double-blind trial, which always sounds like a weird construct. But it's what scientists use. It means neither the person giving the vaccine nor the person getting the vaccine knows what's in the needle. And so any - you might think, oh, well, I've been vaccinated. It's safe to go out and play - behave dangerously. You just don't know.

SOFIA: Right.

PALCA: And so we presume that both groups are behaving in the same way with no additional knowledge.

SOFIA: Yeah. And the other key to this trial is there's not a fixed time, right? It's an event-driven trial. So researchers are kind of waiting for cases of COVID to appear.

PALCA: Right. They did a calculation before they started the study trying to figure out, well, how many cases do we need to see to have some kind of statistical confidence that this vaccine is working? And from a variety of statistical measures, the number they came up with was 164.

SOFIA: Right. When they hit 164, the study has kind of reached its goal.

PALCA: That's right.

SOFIA: OK. So these preliminary results also said that the efficacy was above 90% seven days after the second dose, right? So here's my concern, Joe. We know this virus can hang out for a good bit before it shows up in your body, right? Like, it's got a fairly long incubation window, sometimes longer than seven days. So are they really waiting long enough to see this show up?

PALCA: Yeah. It's a reasonable question. And other studies have decided to make their first look at 14 days. I don't know all the reasons that Pfizer chose seven days. But also remember that this is seven days after the second dose. And the second dose comes 21 days after the first dose. So they're probably capturing at least, you know, some people after at least one injection. And the other thing is they'll be looking at longer time periods. So they may miss a few or may capture a few that they shouldn't have. But I think, in the end, it'll be OK.

SOFIA: And the other thing is, Joe, you know, earlier you said that this vaccine has kept people from developing symptoms. What I'm not hearing is that this vaccine has kept people from getting infected. So you know, isn't it possible that they're missing those asymptomatic cases here?

PALCA: Yeah. No. It's very possible. I mean, the efficacy says we prevented people from getting sick. But we don't know how many people got infected and didn't get symptoms since they're only counting people who did get sick or - and had at least one symptom and were confirmed with PCR.

SOFIA: Right.

PALCA: So they don't know if it's preventing infection, which is important to know because we know that this is a disease that can be spread by asymptomatic people who aren't showing any signs of being sick.

SOFIA: Got it. Got it. And since it's so early, I mean, we still don't know how long this apparent protection or immunity lasts.

PALCA: Yeah. Yeah. It's another open question. I mean, they're looking out through this time frame of 164 cases. But when that comes, you know, that - they are going to follow these people further along. So you know, they will get more data about how long they're protected.

SOFIA: So Joe, what's next for this vaccine?

PALCA: Well, the study will continue and - until they reach this endpoint of 164 cases. And they'll, essentially, become more and more confident that the numbers that they're seeing, the efficacy numbers, are accurate.

SOFIA: Right. And then what happens at that point?

PALCA: Well, we talked about how this is an event-driven trial...

SOFIA: Right.

PALCA: ...But the FDA's guidance has said that there are known side effects to vaccines that usually show up between two and three months after the course of a vaccine.

SOFIA: Got it.

PALCA: So the agency has said they want a minimum of two month's follow-up from at least half the participants so that they can, hopefully, catch these rare side effects if any of them are occurring.

SOFIA: OK, Joe. So that brings me to my last question. You know, this is really fast as far as vaccine development goes. And I know people are concerned about that. So is this a situation in which we're cutting safety corners? Or is it just so fast because, as a country, we're dumping a ton of money on it?

PALCA: Well, I'd say, yes, it's fast because we're dumping a ton of money on it. Both the companies and the countries are spending big. And - but it's also fast because it's become a No. 1 priority. I mean, FDA isn't telling these companies, hey, we'll get back to you, you know, there's a lot of people we have to analyze. No...

SOFIA: Right.

PALCA: ...This is the top of the queue. And as for cutting corners, you know, I don't get that sense. They can't answer all the safety issues with these initial studies. And, I mean, you want to give the vaccine to people as soon as you can, so you can only study some number of people.

SOFIA: Right.

PALCA: And it's quite possible that something that doesn't show up with 40,000 people will show up when you get to 40 million people.

SOFIA: Yeah.

PALCA: So it's not so much cutting corners as it is, you know, trying to get the vaccine out the door as quickly as possible. And remember, the results we've been talking about today are just preliminary. I mean, so there will be more information coming about these results. And it will be a while also before manufacturers can make enough doses of any of these vaccines to start giving them to everyone who might want one.


SOFIA: OK, Joe Palca. We appreciate you. Thank you for this update.

PALCA: Ah, and I appreciate you, Maddie Sofia.

SOFIA: Just a heads up here - we are continuing our COVID coverage on Monday with an episode all about vaccine distribution, who might get the vaccine first and some of the challenges we'll face along the way.

This episode was produced by Thomas Lu, edited by Gisele Grayson and fact-checked by Ariela Zebede. I'm Maddie Sofia. Thanks for listening to SHORT WAVE from NPR.


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