The U.S. Food and Drug Administration has stated that undiluted frozen vials of the Pfizer-BioNTech COVID-19 vaccine can be transported and stored at temperatures that are commonly found in pharmaceutical freezers, for up to two weeks. 

This comes as an alternative to the storage of the vaccine vials at temperatures of -80ºC to -60ºC (-112ºF to -76ºF). Pfizer Inc. had submitted data to the US regulator which stated that its COVID-19 vaccine remained stable after undiluted vials were stored for up to two weeks at standard freezer temperature. However, this alternative storage temperature for frozen vials does not apply to the thawed vials prior to dilution, or the storage of thawed vials following dilution… (FDA, February 25, 2021)