NOEL KING, HOST:
Moderna, a company that's working on a vaccine for COVID-19, says it has some promising early results. A vaccine was given to 45 volunteers - which is not a large sample size, admittedly, but there is a lot of excitement about what happened next. NPR science correspondent Joe Palca is with me. Hi, Joe.
JOE PALCA, BYLINE: Hi. How are you?
KING: Good. Thanks. Why are people so excited about this trial vaccine?
PALCA: Well, it is good news. As you said, it's only 45 volunteers at this point. This is what's called a phase one study, and the main impetus for doing this is to make sure the vaccine is safe. And the good news is that the company is reporting this morning that there were no serious side effects from any of the volunteers who took the vaccine.
KING: No serious side effect sounds like a good thing. Were there any side effects at all that are worth noting?
PALCA: Well, like many vaccines, it caused some soreness when people got injected in the arm.
KING: OK.
PALCA: And three people actually came down with flu-like symptoms. But the company says that all of the symptoms were temporary and resolved themselves very easily.
KING: OK, so much like a normal vaccine.
PALCA: Right.
KING: That seems like a ray of hope. The company, Joe, said that all of the volunteers had, quote, "an immune response" to the vaccine. What does that mean?
PALCA: Well, this is not a study that's trying to see if it can protect patients. But what they can do is that after someone's gotten a vaccine, they can draw blood from that person and look in the blood to see if there are antibodies. And, of course, antibodies are what your immune system does first - or not very first, but among the first things it does is make antibodies to an invading organism, in this case a vaccine. And that's how vaccines work. They provoke an immune response so that if the person is ever actually exposed to the virus, they'll have an immune response ready that can fight it off.
So they saw, from the first 45 patients, that all - or volunteers - all of them had an immune response. That's the good news. Eight of them actually had an advanced immune response, where they were able to show that the virus wouldn't infect cells. So it's all good at this point but all very preliminary.
KING: OK, fair enough. What's next, then?
PALCA: Well, what happens now is they expand the trial, these studies. So in order to find out if the vaccine is effective and preventing the - people from being infected, they have to vaccinate a lot more people because you need to have a certain number of people become exposed to the virus to find out if your vaccine has worked.
So some people will get a vaccine. Some people will get, you know, a placebo, something that doesn't - won't protect them from COVID-19. And then they'll see if there's any difference between the vaccinated group and the placebo group. But you have to have a large enough number of people exposed to the virus for there to be any good evidence that it's actually working.
KING: OK, fair enough. I feel a little wrong asking you this (laughter) because I don't want to get people's hopes up. Do we know when a vaccine could be ready for the rest of us?
PALCA: Well, the company says they're going to start these expanded trials, expanded studies in July. And if they go well, you know, it could be by the end of the year - fingers crossed. Who knows?
KING: Fingers crossed. NPR's Joe Palca, thank you.
PALCA: You're welcome.
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