Why Do COVID-19 Vaccines Have To Be Stored at Different Temperatures?

Scientist getting samples from lab fridge.

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Key Takeaways

  • The Pfizer, Moderna, and AstraZeneca vaccines have different storage requirements in terms of temperature because of the ways they're structured.
  • The Pfizer vaccine has to be kept at a frigid -70 °C, while the Moderna and AstraZeneca vaccines can be kept slightly warmer.
  • Experts anticipate the Pfizer vaccine’s difficult storage requirements will pose a challenge during distribution.

Within two and a half weeks of each other, three big-name pharmaceutical companies—Pfizer (working with BioNTech), Moderna, and AstraZeneca—produced viable COVID-19 vaccine candidates in a development that potentially signals the beginning of the end of the pandemic.

The Pfizer and Moderna vaccine candidates received emergency use authorization (EUA) from the Food and Drug Administration (FDA) in December, and they are being rolled out approximately nine months after the World Health Organization (WHO) officially declared COVID-19 a global public health crisis—the fastest turnaround time in world history. AstraZeneca is also preparing to request an EUA once more trial data is available in the coming weeks.


The previous record-holder, the mumps vaccine, took more than four times as long to see the light of day.

But getting the FDA’s authorization is only the first of several hurdles the companies will face in the race to the finish line. The Pfizer vaccine, whose working name is BNT162b2, has stringent storage requirements that may make it more difficult to distribute large numbers of doses nationwide.

BNT162b2 has to be kept unusually cold—as in about minus 70 degrees Celsius (minus 94 F), or within a range of minus 80 to minus 60 degrees C (minus 112 to minus 76 F). This is chillier than a winter’s day in Antarctica. By contrast, the seasonal flu vaccine has to be kept at a comparatively warm 4 degrees C, or 39.2 degrees F, according to Sheila Keating, PhD, associate professor of laboratory medicine at the University of California, San Francisco School of Medicine.

What This Means For You

Different temperature storage requirements for approved or authorized COVID-19 vaccines may affect which vaccine will be easily accessible to you in the future. But many vaccines with varying levels of requirements are currently in the works.

How Will These Storage Demands Be Met? 

Keating anticipates that these requirements will significantly complicate the distribution of BNT162b2. In order to ensure the efficacy of the vaccine, according to Keating, people will need to be vaccinated at “centralized locations with access to minus 80 degrees Celsius freezers” or dry ice containers.

But this equipment is high maintenance in and of itself. Dry ice containers need “to be replenished regularly and dry ice supply may prove to be difficult to maintain,” Keating says.

Pfizer has preempted criticism of BNT162b2’s design by developing and manufacturing storage units specifically tailored to the vaccine. Roughly the size of a suitcase, these units can carry at least 975 doses and are packed with enough dry ice “to recharge it one more time,” Jessica Atwell, PhD, assistant scientist in the division of global disease epidemiology and control in the department of international health at the Johns Hopkins Bloomberg School of Public Health, tells Verywell.

However, it won’t be feasible to ship them worldwide. 

“Doing that in high-income countries like the U.S. is one thing," Atwell says. "Trying to do that in low- and middle-income countries around the world where even a normal 2 to 8 degrees C, refrigerator-like temperature, can be really difficult in many parts of the world. So it's definitely an implementation challenge.” 

Perhaps the biggest barrier to the widespread distribution of a vaccine that needs to be kept as cold as BNT162b2: There’s no precedent for it. “We don’t currently use any [vaccines] that require minus 70-degree storage,” Atwell says. 

How Does BNT162b2 Stack Up To Its Competitors? 

By comparison, BNT162b2’s rivals—the Moderna vaccine, mRNA-1273, and the AstraZeneca vaccine, AZD1222—are lower maintenance. The vaccine mRNA-1273 needs to be kept at about minus 20 degrees C (minus 4 F, around the temperature of a regular freezer), or a range between minus 25 to minus 15 C (-minus 13 to 5 F), while AZD1222 needs to be kept between 2 and 8 degrees C (between 36 and 46 F), around the temperature of a regular refrigerator.

Their relatively relaxed storage requirements mean that they will likely have a leg up on BNT162b2. AZD1222 will “be significantly more accessible in a lot of places,” Keating says, although mRNA-1273 “is not too difficult to handle” either. 

“[I think] the AstraZeneca vaccine might be better suited for use in different parts of the world," Atwell says. "It's definitely more in line [than BNT162b2 and mRNA-1273] with the vaccines that are already available and used all over the world."

Why Must These Vaccines Be Stored at Different Temperatures? 

The radical difference in these vaccines’ storage temperature requirements has to do with their respective designs. Both BNT162b2 and mRNA-1273 are messenger RNA (mRNA) vaccines, meaning that they were made using fragments of viral genetic material.

Essentially, Atwell says, mRNA vaccines are “lipid nanoparticles that encapsulate the messenger RNA inside” and have a stabilizing effect. She attributes the 50 °C variation in their storage temperature requirements to the “sort of lipid nanoparticles that encapsulates the mRNA.”

AZD1222, on the other hand, is what Keating calls a “viral-vectored vaccine,” meaning that it was made by attaching proteins from the coronavirus to another, harmless virus, such as an adenovirus. In general, according to Atwell, mRNA is less stable—or less tolerant of a range of temperatures—than viruses or viral particles, which explains the difference in storage temperature requirements.

Cold temperatures, Atwell says, are necessary to prevent the mRNA vaccines from degrading, although she believes that both Pfizer and Moderna are currently conducting stability tests to determine whether their vaccines can tolerate higher temperatures. 

“I think there's been a lot of really impressive innovation in the last year in terms of problem-solving some of these challenges,” Atwell says, citing Pfizer’s storage units as an example. “So I think that there will continue to be innovation in the space and that we might be able to come up with new solutions to some of these problems, but it is going to be tricky for sure.” 

The first COVID-19 vaccine candidate to receive an emergency use authorization from the FDA was Pfizer-BioNTech's BNT162b2 on December 11, followed by Moderna's mRNA-1273 on December 18. Distribution for both vaccines in the U.S. has begun.

Despite the distribution challenges they pose, BNT162b2 and mRNA-1273 represent a new frontier in vaccine development as the first mRNA vaccines to be administered to humans, according to Atwell. One silver lining to the pandemic: a scientific breakthrough decades in the making.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.

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4 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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