AILSA CHANG, HOST:

There have been mixed messages out of Washington today about the timing of a coronavirus vaccine. CDC Director Robert Redfield told lawmakers on Capitol Hill that it likely won't be widely available until the summer or autumn of next year. Later, President Trump said the rollout would be much faster. But the thing is finding a safe and effective vaccine might turn out to be easy compared to the monumental task of getting a large number of Americans vaccinated. NPR pharmaceuticals correspondent Sydney Lupkin has been reporting on the Trump administration's vaccine distribution plan, and she's here to walk us through what she found.

Hey, Sydney.

SYDNEY LUPKIN, BYLINE: Hey, Ailsa.

CHANG: So what are public health officials are up against? Like, what are the challenges involved in distributing a vaccine?

LUPKIN: A big challenge is uncertainty. We don't know which of the vaccines will be OK'd by the FDA or when, and they're all different. Operation Warp Speed includes six different vaccines at various stages of clinical testing. The two that seem most likely to be ready first are from Pfizer and Moderna. They're stored at different temperatures, require different kinds of preparation by the health care provider. These vaccines would require two doses. But shots of the Pfizer vaccine would be 21 days apart. For Moderna, we expect it to be 28 days. And we need to be sure that a patient getting the first dose of, say, the Pfizer vaccine doesn't accidentally get a dose of the Moderna vaccine because they're not interchangeable. Paul Mango is the deputy chief of staff for policy at HHS.

PAUL MANGO: This is a really quite extraordinary, logistically complex undertaking. And a lot of uncertainties right now - I think the message we want you to leave with is we are prepared for all of them.

CHANG: OK, so how are they preparing right now?

LUPKIN: Today the Centers for Disease Control and Prevention put out what it's calling an interim playbook for vaccination. It touches on storing, shipping and distributing a coronavirus vaccine as well as an IT system to keep track of everything. And this is a huge collaborative effort. For starters, you've got two federal agencies, the CDC and the Department of Defense. Then the federal government needs to coordinate with states and territories, and, of course, private companies come into play as well. So Operation Warp Speed is coming up with different possible scenarios and doing tabletop exercises to practice.

CHANG: I mean, this is extremely complicated. And just to be clear, we're not all going to get the vaccine at once, right? So how is this distribution going to roll out?

LUPKIN: Well, we know that once the FDA green lights a vaccine, there won't be enough to give it to 300 million Americans. By the end of the year, there could be tens of millions of doses if things go right. Still, the government is going to have to prioritize. The plan is that health care workers, people with underlying medical conditions, the elderly and essential workers will be first. And as for everyone else, the CDC Director Robert Redfield told the Senate committee this morning that most Americans wouldn't receive a COVID-19 vaccine until summer or early autumn of 2021. However, later in the day, President Trump contradicted that timeline. He told White House reporters he thinks the CDC director was confused and that distribution could start as soon as October and is going to go much faster.

CHANG: OK, so what do other public health experts think of this distribution plan so far?

LUPKIN: I mean, the reception has been somewhat mixed. People are happy to see a plan but would like it to include more detail. Former CDC Director Tom Frieden says preparation is good. It's a good thing. But he expected this kind of document a couple months ago. He's glad that McKesson, a large drug distributor, was tapped to help with the vaccine logistics. It proved that it could do this work during H1N1, swine flu, back in 2009.

TOM FRIEDEN: They delivered more than 120,000 deliveries to nearly 80,000 delivery points refrigerated and without a glitch.

LUPKIN: But it took them four months to scale up. He's also concerned about having a sophisticated plan to build public trust considering so many Americans are skeptical of a coronavirus vaccine.

FRIEDEN: If we have a safe and effective vaccine, we need to handle it right not just in terms of the temperature but in terms of the trust so that it can be preserved and used and protective not only in this country but around the world.

LUPKIN: So we'll see what happens.

CHANG: That is NPR pharmaceutical correspondent Sydney Lupkin.

Thank you, Sydney.

LUPKIN: You bet. Transcript provided by NPR, Copyright NPR.