Moderna's COVID-19 vaccine has ‘competitive advantage’ over Pfizer's — here’s why

·5 min read
A biologist in Brazil takes a coronavirus DNA sample from the freezer.
A biologist in Brazil takes a coronavirus DNA sample from the freezer. (Photo by Pedro Vilela/Getty Images)

As experts celebrate the 94.5 percent efficacy rate that Moderna has reported for its COVID-19 vaccine in phase III trials, immunologists are highlighting a separate fact that may give the U.S. drugmaker a “practical advantage” over its competitors: storage needs.

Both Moderna and Pfizer have reported 90 percent efficacy or above, a number that far exceeds the Food and Drug Administration’s 50 percent cutoff for approval of a COVID-19 vaccine. But one of the chief concerns in the wake of Pfizer’s news was the fact that its vaccine needs to be transported in ultra-cold temperatures and stored at -94 degrees Fahrenheit. Moderna’s, in contrast, can be transported and stored at just -4 degrees Fahrenheit, a temperature that can be achieved through a standard freezer.

“It’s going to be a logistical challenge for Pfizer, the likes of which no company in the world has ever faced because we've got a vaccine that the entire world wants,” Dr. Richard Kennedy, an immunologist and co-director of the Mayo Clinic’s Vaccine Research Group, tells Yahoo Life. “And if there are two doses needed, you're talking 16 billion doses, how are you going to get ultra cold freezers throughout the world in areas that have power shortages or no power at all?”

To clarify how Moderna’s vaccine differs, and why it may have an advantage, here’s what you need to know.

In general, mRNA is tough to store

In an earlier interview with Yahoo Life regarding the Pfizer vaccine, Dr. Gregory Poland described why keeping the vaccine — which is made with a novel technology called messenger RNA — cold is so critical. “For [Pfizer’s] particular vaccine, once it heats up to a certain temperature ... then the vaccine becomes less effective,” said Poland. “That's been one of the difficulties in developing an mRNA vaccine.” Kennedy agrees, saying, “RNA is a very finicky molecule and so it needs to be kept at cold temperatures.”

According to the Wall Street Journal, Pfizer plans to use “reusable, temperature-controlled containers” that it loads on “two dozen trucks per day,” with the goal of shipping more than seven million doses to airports near two distribution sites, one in Michigan and the other in Belgium. But the containers only allow 10 days of storage. Poland worries about how they will be stored after that. “That’s going to be very difficult in the U.S., likely impossible outside of the West, because nobody has storage facilities for this.”

Moderna may have upgraded the “formulation” of its vaccine to make it easier to store

At this point, it’s unclear why Moderna’s vaccine has a higher threshold for survival, but Kennedy says that its composition may play a role. “It might come down to the actual chemical structure of the RNA and how they stabilize it,” Kennedy tells Yahoo Life.

In a call with reporters on Monday, Harvard University immunologist and infectious disease expert Dr. Barry Bloom further clarified the discrepancy. “There is clearly an upgrading of the formulation of the Moderna vaccine that no longer requires ultra-cold temperatures to maintain stability, which is the characteristic of the Pfizer-BioNTech vaccine,” said Bloom, adding later, “There's a practical advantage at the moment for the distribution of the Moderna vaccine.”

This means that while Pfizer’s vaccine requires a specialty freezer, Moderna’s does not

News of the ultra-cold storage needs of the Pfizer vaccine last week reportedly set off a “wave of freezer panic buying” nationwide, according to Reuters, with doctors racing to buy specialty freezers in the event that they need to store it. But with Moderna’s candidate, even those in less financially stable states and regions will likely already have access to the appliances needed to keep it safe. “A regular freezer can hold the Moderna vaccine; a regular freezer is not nearly cold enough for Pfizer’s,” says Kennedy.

Bloom agrees. “It will clearly be something that every physician's office, every clinic will have a refrigerator that can keep the vaccine cold for various periods of time and can keep it for six months in the freezer compartment of ordinary refrigerators, as opposed to ultra cold freezers,” said Bloom. He added that ultra-cold freezers “are not going to be available in very large parts [of the world] — particularly in rural places.” This could mean that the Pfizer vaccine will be “much more restricted for global distribution in low- and middle-income countries.”

Overall, the concept underscores the need for many vaccine options

With over 54 million cases of COVID-19 worldwide, including 11 million in the U.S. alone, experts say it’s less about which company has a better option and more about increasing the number of them. “It’s going to be a distribution challenge for [Pfizer] and so that's one reason I think it's important that we keep having vaccines come through the pipeline,” says Kennedy. “There will be vaccines that have different storage conditions, much like Moderna's, and in the end no one company is going to be able to produce enough doses for the entire world. So we're going to need a lot of companies working on successful vaccines.”

For the latest coronavirus news and updates, follow along at According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please reference the CDC’s and WHO’s resource guides.