STEVE INSKEEP, HOST:
Let's take the temperature, so to speak, of the effort to distribute a vaccine. Two companies have now announced they have coronavirus vaccines shown to be 90% effective or more. One of them comes from Pfizer, and one comes from Moderna. Immediately after the news of Moderna's vaccine broke on Monday, the company gave a presentation to the people who would have to distribute such vaccines. Both of them have to be kept frozen, which means you cannot just ship and store them like other products.
A lot of lives rest on how that particular detail is addressed, so NPR's Selena Simmons-Duffin has been looking into it. Good morning.
SELENA SIMMONS-DUFFIN, BYLINE: Good morning, Steve.
INSKEEP: Why do the vaccines need to be kept frozen?
SIMMONS-DUFFIN: Well, both of these vaccine candidates are what's called messenger RNA vaccines, and mRNA is very unstable. So to help explain what that means, here's an analogy. Think of the vaccine like a melty chocolate bar. To stabilize the vaccines, these drug companies used modified building blocks, or nucleosides, which would kind of be like changing the chocolate recipe so it's less melty. And then the coated it...
INSKEEP: And not on my 5-year-old's fingers quite as much. OK, go on. Go on.
SIMMONS-DUFFIN: (Laughter) Right. So then they coated it with something called lipid nanoparticles. Margaret Liu explained this to me. She's a vaccine researcher who chairs the board of the International Society for Vaccines.
MARGARET LIU: That formulation helps protect the RNA. It's kind of like putting your chocolate inside a candy coating and you have an M&M, so the chocolate doesn't melt.
SIMMONS-DUFFIN: So then the freezing is also done to protect the RNA and make the vaccine more stable. It's the same concept as freezing food so it doesn't spoil. Although only Pfizer's vaccine requires ultracold conditions - that is minus-70 degrees Celsius, which is extremely cold, colder than winter in Antarctica. And that presents challenges.
INSKEEP: Wow, yeah. One of them would be a normal freezer; the other would be this extreme freezing situation. Why would that be?
SIMMONS-DUFFIN: Well, we don't really know. The data isn't public. All we have is these companies' statements. Moderna says that its vaccine can be distributed at minus-20 degrees Celsius, which is regular freezer temperature. Once it's thawed, it can be refrigerated for up to a month, and you can even leave it at room temperature for 12 hours. The Pfizer vaccine is more complicated because it has to be stored at ultracold temperatures, and the company will use specialty shipping containers that can be refreshed with dry ice. But once the vaccine's thawed, it only lasts in the refrigerator for five days.
INSKEEP: What are the implications of those freezing requirements?
SIMMONS-DUFFIN: So what this means is that immunization managers, who are in each and every state, are expecting they're likely going to get both of these vaccines, and they'll have to figure out where to send them - probably to different kinds of places. So Christine Finley is the vaccine manager in Vermont. She's still finalizing the state's vaccination plan. She told me it might make sense to send the Pfizer vaccine, which comes in huge quantities and requires the dry ice and the specialty freezers, to be sent to big population centers.
CHRISTINE FINLEY: If you have a large university where you're going to be able to reach a larger number of people, that would make sense that you might consider distributing your ultracold there. And then in areas where it might be more difficult to use up such a large order or they may not have the storage, you've now got another option.
SIMMONS-DUFFIN: She says especially at first, when there are limited doses, they need and want as much stock of vaccine as they can get.
INSKEEP: When there are limited doses, they'll go, well, not to the general population at first, right?
SIMMONS-DUFFIN: Right. The first limited doses will go to frontline health workers. They're the people most at risk. And then other groups like seniors and people with conditions that make them more likely to get seriously sick. And the general public will get it likely many months after that, which is why public health experts are frantically trying to get the message across that people still need to social distance and hand-wash and wear masks, especially now that the virus is spreading so much across the country.
INSKEEP: NPR Selena Simmons-Duffin, thanks for your reporting.
SIMMONS-DUFFIN: Thank you.
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