Why Does the COVID-19 Vaccine Have to Be Kept So Cold?

Plus, how to make sure yours has been properly stored to remain effective.

More than two million doses of the two new vaccines against COVID-19 have been put in people's arms since December 14. But racing the shots to the frontline health care workers hasn't been an easy feat—the Pfizer-BioNTech vaccine specifically must be stored at subzero temperatures, creating a logistical puzzle of dry ice and specialized freezers. And while the Moderna vaccine remains stable at slightly balmier temperatures, it too must stay frozen throughout shipping and long-term storage.

So what's the deal with these cold storage requirements? Here's why it's critical that the new COVID-19 vaccines are kept super chilly and how to make sure the one you get has been stored properly.

Group of vaccines for Covid 19 virus in a block of ice for preservation and transport.
Adobe Stock

Why do COVID vaccines need to be kept so cold?

It has to do with a very important ingredient: messenger RNA (or mRNA). The mRNA in the vaccines is genetic material that teaches our immune cells how to make the spike protein found on the virus that causes COVID-19, according to the Centers for Disease Control and Prevention (CDC). The immune system responds by creating antibodies against that specific spike protein, ultimately learning how to protect the body against the virus in the future.

By their very nature, mRNA molecules are unstable—if they hung out for a long time, our cells could accumulate harmful levels of the proteins they help create.

"mRNA rapidly degrades. There are also enzymes in the environment and all around us that break down mRNA," Lisa Morici, PhD, associate professor in the microbiology and immunology department at Tulane University School of Medicine, where she studies novel vaccine platforms, tells Health.

Vaccine-makers also coat the mRNA in lipid nanoparticles. These tiny bubbles of fat help carry the mRNA to our cells and offer a degree of protection against enzymes that could destroy the fragile genetic material.

"It's like an M&M," Timothy Lise, PharmD, executive director of pharmacy services for New Jersey's Atlantic Health System, where he has served an integral role in distributing the COVID-19 vaccine, tells Health. "If you have chocolate in your hand, it's going to melt, but with the candy coating on the outside, it doesn't."

The lipid nanoparticle coating isn't quite enough to protect the mRNA, though. That's where the cold storage comes into play. The enzymes that break down mRNA "don't work at really, really cold temperatures," explains Morici.

That means between -13 degrees Fahrenheit and 5 degrees Fahrenheit for the Moderna vaccine and a downright arctic -112 degrees Fahrenheit to -76 degrees Fahrenheit for the one from Pfizer. The specific lipid nanoparticle formulas, which are kept secret by the drugmakers, determine just how cold the vaccines must be kept, hence the different storage requirements.

How is the COVID-19 vaccine kept cold?

Getting vaccines to patients safely depends on the "cold chain," or the temperature-controlled hand-off of the shots each step of the way from the manufacturer to shipping centers, then onto planes and trucks to the clinic.

Since Moderna's vaccine is safe at standard freezer temperatures, it doesn't require extraordinarily special handling beyond what's already available in the cold chain, the company has said. Distributing it should be relatively straightforward.

The Pfizer vaccine is another story, though. It's packed in dry ice (similar to how the popular Dippin' Dots ice cream is packed) and shipped in special thermal containers, complete with sensors that track location and temperatures, to make sure it stays within the required temperature range. Once the vaccine arrives at its destination a day or two later, Pfizer recommends popping it into an ultra-low-temperature freezer—expensive, specialized equipment that's often not available outside of large urban hospitals, per STAT. (FYI, Dippin' Dots are also stored in specialized ultra-low temperature freezers—and vaccine distributors, hospitals, and pharmacies have even reached out to the company to rent equipment for COVID-19 vaccines, per Popular Science.)

Healthcare facilities also have the option of keeping the Pfizer vaccines in their thermal containers and adding fresh dry ice every five days for up to a month, or storing it in a refrigerator for up to five days. But between fears of a dry ice shortage and the scheduling difficulties of ensuring that every thawed dose goes into someone's arm before it expires, distributing the Pfizer vaccine to some communities (particularly rural areas) is riddled with challenges.

"It's a lot of strain on resources and on the supply chain," says Lise. "As time goes on and the technology develops further, they'll make sure they can get the vaccine into the hands of anyone with a fridge—places that don't have the types of resources that large healthcare systems do."

How can you tell if your vaccine has been kept cold enough?

As the COVID-19 vaccines make their way through the cold chain, their temperatures are being tracked. They're also being monitored at their destinations on a daily basis using a digital data logger with a probe that can accurately reflect the temperature of a vaccine.

Double checking that the vaccine you get has been kept cold enough could be as simple as asking for those temperature logs, says Lise, adding that pharmacy managers already keep track of this information for state inspectors.

"This is a patient-centric model and patients need to feel confident in the process and safety of the vaccine," he says. "If a patient asks us, we can provide all of that temperature data. I'd print it out for them."

It's unclear at this point if every health facility will offer that level of transparency, though. In some cases, patients may need to simply trust the system and the safeguards it has in place.

"We have to put our faith in the doctors and pharmacies administering the vaccine to us," says Morici. "They have the quality controls in place to make sure they're following the requirements of the manufacturers."

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDC, WHO, and their local public health department as resources.

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