Novavax, a vaccine maker in Maryland, is becoming the 10th coronavirus vaccine candidate to enter the final phase of testing, called phase 3.

The trial is taking place in the U.K., where researchers plan to enroll up to 10,000 adults of various ages in the next four to six weeks. Half the participants will get a placebo and half will get the company's vaccine.

At least a quarter of participants will be over the age of 65, the company says, and it will also "prioritize groups that are most affected by COVID-19, including racial and ethnic minorities."

The company expects to start a U.S. trial with 30,000 volunteers in mid-October.

Companies are working to develop vaccines at an unprecedented pace. Many Americans are concerned about the safety of a fast-tracked process, done under the purview of a president who contradicts his own health officials.

Novavax was one of nine companies to publicly pledge to not submit their vaccines for Food and Drug Administration review until they've been shown to be safe in trials. Novavax has never before brought a vaccine to market.

"I don't think that there's going to be any chance that there's going to be some shortcut made," says Gregory Glenn, Novavax president of research and development.

He talks with NPR's All Things Considered about why the vaccine trial is taking place in the U.K. and how to reassure Americans that any vaccine will be safe. Here are excerpts:

Why did you choose the U.K. for your vaccine trial, especially rather than here in the U.S., where Novavax is based?

We went to the U.K. because they have a very good trial network and we felt that the attack rate would be high, the transmission would zoom up in the wintertime, which it looks like it's going to do. ...

If we succeed there, we will get a license for our vaccine in the U.K. and Europe, and then that opens the door for many countries that otherwise would not require testing, but normally they would rely on the package of information either from the FDA or Europe for them to deploy their vaccine in their own country. So this opens up the door for a lot of the world in terms of a regulatory approval and licensure for them to take advantage of a highly competent regulatory authority that we have in the U.K.

And theU.K. infection rate zooming up, as you put it, is a good thing for you because you're looking for places in the world where a lot of people are infected and your vaccine might work on them.

Exactly. The way it happens in the trial is you need cases, right? So you obviously couldn't prove anything if there are no cases. The more cases in your trial setting, the faster you accumulate the evidence that the vaccine works.

The CEO of Novavax was one of nine pharmaceutical executives who came together to reassure the public in a published statement that their vaccines will be safe and effective, not a rush job that would potentially harm anyone's health. It is stunning in a way that they would feel they have to do that. Would you comment on the fact that they felt they had to?

Look, I have mixed feelings because our M.O. here is to be transparent. We know the FDA [has] a formula that they're not going to deviate from. So I don't think that there's going to be any chance that there's going to be some shortcut made. But there's so much worry in so many areas about vaccination that ... it's reasonable to reassure the public that's the case.

And it's interesting now that this is such a high-profile topic. People are interested in the details, which they never were. They didn't know how vaccines work. They didn't know how you did, that you even did trials to show how they work, etc. So there's a lot of scrutiny on that. And anything we can do to help the public confidence is good.

But this is also a vaccine trial that has been more politicized, maybe, than any other one. I'm interested in how the politics of this are affecting the business and science aspect of this for you.

I kind of ignore it all. My team is focused on generating convincing evidence that the vaccine is safe. The FDA has laid out the pathway to approval. There's nothing unclear about what has to be done. I'm a pediatrician. I believe vaccinations have very positively impacted the world. And so that's how I look at the day. My day is, I'm going to get up and create that evidence that will lead to utilization and saving the world.

Art Silverman and Christopher Intagliata produced and edited the audio interview.

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