Why Do the COVID-19 Vaccines Need to Be Stored in Frigid Temperatures? A Doctor Explains

Pfizer-BioNTech’s vaccine needs to be stored at a shocking -94°F. Here’s what that means for a distribution plan.

covid 19 vaccine bottles inside ice
Andriy OnufriyenkoGetty Images
  • The Pfizer and Moderna COVID-19 vaccines must be stored at -94°F and -4°F respectively to remain effective.
  • The vaccines rely on mRNA technology, which requires intensely cold storage.
  • Even the most well-equipped hospitals could face problems storing the current vaccines, but future options could bypass subzero storage entirely.

    The most difficult stage of deploying the initial COVID-19 vaccines—actually creating and testing them—is mostly over less than a year after the coronavirus pandemic began, the fastest such achievement in history.

    “Nobody in the vaccine field, if you had asked them in March, would have said, ‘Yeah, we’ll have a vaccine by the end of December,’” says Kawsar Talaat, M.D., an infectious disease doctor, vaccine researcher, and assistant professor in the department of International Health at Johns Hopkins University. “The fact that we managed to get vaccines tested and evaluated, and that they have shown to be so incredibly effective, is really amazing.”

    However, we’re not in the clear yet: Shipping and storing the vaccines is a massive, costly challenge. Both Moderna’s and Pfizer-BioNTech’s vaccines, which have been granted Emergency Use Authorization from the Food and Drug Administration, must be kept at subzero temperatures until they reach their destinations, a technical snag that could hinder immunization efforts. As Americans anxiously await their chance to receive their two doses, the country’s public health system is putting together a very chilly distribution plan.

    First, the COVID-19 vaccines must be stored at frigid temperatures.

    The two approved COVID-19 vaccines require seriously low temperatures to remain viable, but this isn’t unusual. According to the Pan American Health Organization, a specialized international health agency for the Americas, most vaccines are stored between -58°F and 46°F—but both options are on the low end of the scale.

    Pfizer’s vaccine must be stored and shipped at a shocking -94°F to remain effective. Moderna’s vaccine, meanwhile, should be stored at -4°F. If these temperatures are not maintained through every stage of the cold chain, certain elements could degrade, leaving the vaccine useless. Only at the final stage of the journey, when they’re thawed to perform immunizations, can vaccines come out of that deep freeze.

    The Moderna vaccine can be stored up to 30 days in normal refrigerator conditions; the Pfizer vaccine, up to five days. Both have a cold-storage shelf life of up to six months, so doses don’t need to be used immediately, as long as they’re stored properly.

    Their storage temperatures are probably so different due to the development and manufacturing processes, Dr. Talaat says, but because their formulations are private, there’s no way to know for certain.

    Why do the COVID-19 vaccines need to be kept so cold?

    The ultra-cold storage temperatures are a result of both vaccines’ mRNA technology. Any vaccine of this type is relatively fragile, Dr. Talaat explains, meaning they should be kept at lower temperatures. Heat them up too much and their potency (or the vaccines themselves) could degrade.

    “When we create biological substances, we want to prevent anything from happening to them, so often we’ll put them into really cold temperatures to keep them stable,” she says. “That helps them stay [effective] for as long as possible.”

    When vaccines are developed, they go through stability testing—basically taking them out of the freezer and checking that they’re holding up well. Lower storage temperatures generally equate to higher stability, at least at first, Dr. Talaat explains. In order to store them at higher (but still cold) temperatures, researchers either prove that vaccines remain effective at the new temperature or add certain stabilizers to their ingredients list.

    Neither COVID-19 vaccine has been around long enough for thorough stability testing resulting in more convenient temperatures. “You want to make sure it works before you get there,” Dr. Talaat says. Because experts have worked so hard to get these vaccines out quickly, they haven’t necessarily had the spare time to check what could keep the vaccines stable at higher temperatures. (After all, more than 300,000 Americans have died of COVID-19 this year.)

    Now that researchers have the benefit of time, future generations of the vaccine will likely be much easier to store; some COVID-19 vaccines already in development don’t require such intense freezing to survive. The next generation of vaccines, including AstraZeneca’s, which is kept at normal refrigerator temperatures, already offers a glimmer of hope for easier storage.

    How will storage temperature requirements impact initial vaccine distribution?

    The types of freezers that can keep the current COVID-19 vaccines stable, especially Pfizer’s, are expensive and generally only found in hospitals and labs. “A clinic, a nursing home, or even [regional] health departments may not have freezers that can hold things at -94°F,” Dr. Talaat says.

    Transportation and storage are two of the biggest hurdles for the worldwide immunization rollout. A Reuters report from last month called the vaccine’s complex requirements “an obstacle for even the most sophisticated hospitals in the United States.” Rural and underfunded healthcare providers without the resources to improve their cold storage face even greater obstacles.

    Since Moderna’s vaccine holds up well in normal freezers, Pfizer’s subzero option will be the most difficult to ship. The company is currently shipping its vaccine in so-called “pizza trays,” which hold 195 vials that remain stable for a few weeks, thanks to a steady supply of dry ice.

    Right now, the Pfizer vaccine is being stored at the company’s production facilities and at “freezer farms,” huge storage sites equipped with specialty freezers about the size of refrigerators. (Interestingly enough, one of the only companies producing freezers that reach such low temperatures is Dippin’ Dots, which ships and stores its signature ice cream at -40°F.)

    Vials of Moderna vaccine are still difficult to ship, but have caused fewer headaches so far. “You go from specialty freezers that only labs and hospitals have to freezers that any clinic will have,” Dr. Talaat explains. Both vaccines are already being distributed to government officials, healthcare workers, and nursing home residents.

    Even with such finicky storage, experts are breathing a sigh of relief that distribution is finally underway. “I am so happy to have a vaccine, even when it’s stored [so low], that is 95% effective and can hopefully make a dent in this horrible pandemic, rather than waiting for one that’s stable in a refrigerator, but having to wait longer,” Dr. Talaat says. “I’m just so glad that these vaccines are available.”


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