From the Atlantic:
The two leading vaccine candidates in the U.S.—one developed by Moderna, the other by a collaboration between Pfizer and the German company BioNTech—have progressed so quickly to clinical trials precisely because they are the fastest to make and manufacture. They rely on a novel vaccine technology whose advantage is speed, but whose downside is extreme physical fragility. These vaccines have to be frozen—in Pfizer/BioNTech’s case, at an ultracold –94 degrees Fahrenheit, colder than most freezers—which will limit how and where they can be shipped. The ways these vaccines are formulated (without added preservatives) and packaged (in vials that hold doses for multiple people) also make them easier to develop and manufacture quickly but harder to administer on the ground.
