Pfizer’s vaccine needs to be kept at a temperature of -70 degrees Celsius (close to -100 degrees Fahrenheit) or else it risks losing its effectiveness. If that sounds chilly, it’s even colder than you might think—colder even than winters in Antarctica. The other COVID vaccine frontrunner, Moderna—which is set to be reviewed in the next week—only needs to be kept at -20 degrees Celsius, in comparison. So unlike the Moderna vaccine, Pfizer’s cannot be kept in a regular freezer, as they don’t typically reach temperatures that low. And for more vaccine concerns, These Are the Only People Who Shouldn’t Get the COVID Vaccine. But why does Pfizer’s vaccine need to be kept this cold? According to NPR, the two COVID vaccine frontrunners use messenger RNA (mRNA) to help human bodies create a particular coronavirus protein, which can set off an immune response if COVID enters the body. As it turns out, mRNA vaccine technology is so new that no mRNA vaccine has ever been approved by the FDA. Unfortunately, mRNA can also be “easily destroyed,” which adds complications as the vaccines need to stabilize this molecule, Margaret Liu, a vaccine researcher who chairs the board of the International Society for Vaccines and specializes in genetic vaccines, told NPR. This is why the vaccines are kept at cold temperatures, but we don’t know exactly why Pfizer’s levels are so much lower than Moderna’s because the specific formulations have not been disclosed. “It just comes down to what their data is,” Liu said. “If their data shows that it’s more stable at a certain temperature, that’s it.” And for more on the spread of coronavirus, Dr. Fauci Says This One Thing Could Spread COVID More Than Anything Yet. Debra Kristensen, a 30-year veteran of vaccine innovation and supply chains at PATH, an international nonprofit focused on public health, told NPR that distributing the Pfizer vaccine is possible, but it will also be “much more expensive and more difficult,” especially because it will require the need for specialized freezers. “I believe it can be done,” Kristensen told NPR. “Ebola vaccine, for example, was successfully used in a few African countries and also required this ultra-cold chain storage.” And for more up-to-date information, sign up for our daily newsletter. Pfizer, in turn, has tried to make this complication as uncomplicated as possible. The manufacturer has designed its own packaging to keep the vaccines at cold temperatures with dry ice so that they can be stored for up to 15 days without these specialized freezers—which may be a helpful innovation if the vaccine gets approved in the next few days, before distributors can acquire the right freezers. And for more on vaccine distribution, Here’s How to Tell When You’ll Be Able to Get the COVID Vaccine.ae0fcc31ae342fd3a1346ebb1f342fcb