PBS高端访谈:新冠疫苗究竟何时问世?（在线收听）

Sreenivasan: With new coronavirus cases at a record high, the race for a covid-19 vaccine is setting a record pace. But finding a vaccine and making it through the various stages for approval are two different things. I recently spoke with Propublica reporter Caroline Chen about the ambitious timeline and unpredictability of clinical trials. At this point, there seems to be a lot of optimism for people to say, you know what, life is going to get back to normal when I get a shot in the arm, when there's an approved vaccine. I've heard it's just around the corner. But you talked to a lot of experts, and it's not going to be that simple. 

Caroline Chen: I did talk to a lot of experts and there is optimism that we will eventually have a vaccine for the coronavirus. There might have to be some managing of expectations over how soon, exactly, that will be. The trials will take however long they will take to run. And I asked a lot of people, what are you unwilling to compromise on? And what all the experts said to me is, we don't want to compromise on that phase three trial. 

Sreenivasan: The phase three trial is where we have a very large population, thousands of people take it at the same time. Some get the vaccine, some don't get the vaccine. And then, you kind of wait to see, what? What goes possibly wrong?

Caroline Chen: So, the phase three trial is exactly what you said. It is a large trial. So, the first one that's going to happen in the U.S. with the moderna vaccine is planned to be 30,000 people...half get the vaccine, half get the placebo. And then, you just wait and see how many people get sick in the vaccine arm versus the placebo arm. And all this time, you're tracking to see and monitor to make sure that there are no dangerous side effects. That's really important. You want to see what happens and see how many people get sick in the vaccine arm versus the placebo arm and compare those numbers. 

Sreenivasan: One of the things that people are confused by is, well, if there's not an approved vaccine yet, I've also heard that there are companies already manufacturing vaccine. I mean, is that to try to address this idea that even when one is approved, not everybody's going to have access to it right away? 

Caroline Chen: So, typically, what happens in non-pandemic times is that a manufacturer will only make just enough vaccine as they need to run a clinical trial. So, what's happening now is, they are starting to mass-manufacture even while the trials are starting. And so, this could potentially mean that you're going to waste a whole lot of vaccine because if you run the trial and it's not successful, you're just going to have to throw it all away. But if a trial is successful, the minute that the trial is completed, we can have millions of doses on hand. But at the same time, I think we should still be clear that millions of doses on hand is not going to be billions of doses on hand. So, we're still not going to have sort of this, you know, one glorious day where the vaccine is approved and every single person on the planet can immediately get their shot that single day.

Sreenivasan: How is the coronavirus vaccine that we might come up with different than the flu vaccines, which have different levels of efficacy year after year? 

Caroline Chen: There is one lucky break that coronavirus vaccine manufacturers have had so far, which is, so far, a spike protein...which is the part that engages with the human cell...our understanding is that that part hasn't mutated much at all. So, if that's the part that you're really making the vaccine for, that's the key part, and it hasn't changed a lot. Our expectation is that, if we make a successful vaccine for that part, it should likely work. 

Sreenivasan: The administration says they have this warp speed program, and they hope to have something up and running by January of next year. The experts you spoke to, is that accurate? Is that optimistic? 

Caroline Chen: I think the most optimistic people I talked to said it is possible that we will have some vaccine by the end of the year. If everything goes well, we could have a few million doses by the end of the year, which can be prioritized to the people who need it most. And then, for the rest of us, we're going to have to wait for 2021, and we might have hundreds of millions of doses sometime in 2021. This is in the best case scenario timeline, where the trials all work. There are other people who said to me, you know, I hate over-promising. so, I talked to Dr. William Schaffner...he is a longtime vaccine expert...and he just said, you know, I hate it when the government over-promises because then the fear is that we will under-deliver. And he said, I wish the messaging was just, 'we are working on this as hard as we can, and...but we have to get this right.' And he refused to give me a timeline. So, depending on who I talk to, the timeline's varied. 

Sreenivasan: Even best-case scenario, even if I get a vaccine sometime next year, how do I know how long it works? 

Caroline Chen: You cannot know by running a phase three trial how long somebody will be protected by the vaccine. The only way to know how long protection lasts is to track them over time. You know, different vaccines that we have on the market today, some of them require booster shots, some of them don't. And so, we will not know, and we will have to find out along with the rest of the planet. 

Sreenivasan: If we don't know what...how good the vaccine is going to be, how long the antibodies are going to last, there's still a bit of uncertainty here. 

Caroline Chen: So, Dr. Paul Offit, who is a veteran vaccine scientist, said to me, the proof is in the pudding, and the pudding is a phase three trial. So, we will get some very concrete answers from the phase three trials, which are how safe is the vaccine, at least in a big pool of participants; and how effective is it? So, we will get some answers from the phase three trial, which will be really important answers. We won't get some answers. We won't get the answers of how durable is the vaccine over, you know, many months and many years, for example. 

Sreenivasan: Caroline Chen of Propublica, thanks so much. 

Caroline Chen: Thanks for having me.