DAVID GREENE, HOST:
Well, we have good news this morning on the vaccine front. Pfizer said today its experimental vaccine was 90% effective in preventing COVID-19. The pharmaceutical giant and its partner BioNTech made the announcement this morning after an analysis of trial volunteers. And NPR science correspondent Joe Palca has been following efforts to develop a vaccine. He's with us now. Good morning, Joe.
JOE PALCA, BYLINE: Good morning, David.
GREENE: Well, I mean, tell us how big a deal this is, how these trials went for Pfizer and what they found here.
PALCA: Well, it's a pretty big deal on a number of fronts because this vaccine is what's known as an mRNA vaccine. It's based on some of the genetic material in the virus. And there's never been an mRNA vaccine tested at this level and shown to be effective at this level. So it's a - pretty remarkable for that reason.
This study involved almost 44,000 volunteers around the world. And the way it works is half of the volunteers get two shots, and the shot contains the coronavirus - approximately half - of the vaccine. And the other group gets two shots, but there's nothing in the - there's nothing in the needle. It's just saltwater. And the idea is, well, how many people in the group that got the placebo got sick versus how many people in - the people who got the vaccine got sick? And the answer is - well, they didn't give exact numbers, but they had 94 cases of illness in the people who were in the study, and more than 90% were protected, or the efficacy was 90%. So...
GREENE: Wow.
PALCA: ...It's good news. It's an effective vaccine. Sometimes vaccines are only 50% effective, and they're still considered usable. So this is good.
GREENE: Well, you mentioned the 50%. I mean, the FDA has said it would require vaccine to be at least 50% effective in large clinical trials before they'd think about authorizing it for emergency use in this pandemic. I mean, is that the next step? Does Pfizer now go and request an FDA authorization?
PALCA: Yes, they will. But they have agreed with the FDA that they will wait until at least half of the participants in the trial have been followed up for two months. So why is that? There are side effects that are associated with vaccines that are known. Some of them are serious; some of them are not so serious. But they usually, not always, but usually show up within two months of the final of the two doses of a vaccine. So the FDA has said we want to see two months of follow up from at least half of your participants before we consider granting you this emergency use authorization, which isn't approval. But because we're in an emergency situation with the pandemic, the company would be allowed to expand who gets this much more broadly.
GREENE: OK. So there's going to be some waiting before that next step. And then the big question, of course, is even if this vaccine is developed, I mean, how many doses can be available around the world? What is Pfizer's ability to actually manufacture this on a large scale?
PALCA: Well, I should say they expect to have that safety data by the third week of this month, so it's not too far off. The projections are that they expect to make 50 million vaccine doses worldwide by 2020. Remember, that's two doses per person, so that's 25 million people - or 1.3 billion doses in 2021, which would be closer to 600 million people, but still, a lot of doses available.
GREENE: All right. Good news on the vaccine front. Of course, we'll be following this so closely. NPR's Joe Palca.
Thanks so much, Joe.
PALCA: You're welcome. Transcript provided by NPR, Copyright NPR.
