Shares of COVID-19 vaccine developers Moderna (MRNA -1.75%), BioNTech (BNTX -0.61%), and Pfizer (PFE -1.82%) have fallen this week after presentations to the Centers for Disease Control (CDC) revealed that requirements for cold storage of mRNA-based vaccines may limit their availability in the early days of distribution.

Representatives from Moderna and Pfizer presented to the CDC's Advisory Committee on Immunization Practices on August 26, describing the "cold chain" needed to distribute their vaccines, a capability that will need to be in place this year and may require specialized equipment. Both vaccines require shipment at freezing temperatures, but more extreme requirements for the vaccine being developed by Pfizer and BioNTech could limit administration of it to larger sites, such as hospitals.

Rows of vaccine vials.

Image source: Getty Images.

Moderna said that its vaccine will be shipped at minus 4 degrees Fahrenheit and can be kept at refrigerator temperatures for up to seven days at the administration site. Pfizer's vaccine, though, must be maintained at minus 94 degrees during shipment and long-term storage, and must be used within 24 hours of thawing.

Pfizer's shipping requirements can be met using special containers that use dry ice and that can keep the liquid cold for up to 10 days if unopened. But the requirement to use the vaccine within a day unless the packaging is kept cold with replenished dry ice has the CDC planning for the scenario in which it would only be shippable to administration sites that have larger patient volumes.

Supply-chain challenges for vaccine distribution, especially in rural and in underdeveloped areas of the world, may put mRNA vaccines at a disadvantage to competitors, a possibility investors seem have considered in the last few days.