The U.S. drug regulator said Thursday it will allow the coronavirus vaccine developed by Pfizer Inc. to be transported and stored for up to two weeks at conventional freezer temperatures instead of the ultracold conditions previously required.

"The alternative temperature for transportation and storage will help ease the burden of procuring ultralow cold storage equipment for vaccination sites and should help to get vaccine to more sites," the U.S. Food and Drug Administration said in a press release.

A nurse prepares a Pfizer BioNTech COVID-19 vaccine in Paris on Jan. 18, 2021. (Getty/Kyodo)

Before Thursday's announcement, the FDA had required the vaccine to be kept in an ultracold freezer at temperatures between minus 80 C and minus 60 C for a maximum of six months.

With the change, vaccines may now be stored at minus 25 to minus 15 C for up to two weeks, the regulator said.

Pfizer is expected to seek similar approval from regulators in other countries. The vaccine developed by the U.S. pharmaceutical giant and its German partner BioNTech SE has been administered in Japan and other countries.

The Japan unit of Pfizer said Friday in Tokyo it has begun discussions with Japanese drug screening authorities on changes in conditions for the use of its COVID-19 vaccine.

Japanese health minister Norihisa Tamura told a press conference his ministry will thoroughly examine an expected request by Pfizer to allow vaccine storage at higher temperatures.

"If (the requested changes are) appropriate, we will include them in documents attached (to the vaccine) and inform local governments" in charge of administering vaccines, he said.

Last week, the two companies said they have submitted data to the FDA showing their vaccine remains stable for a total of two weeks when stored at minus 25 C to minus 15 C, which they say are temperatures more commonly found in pharmaceutical freezers.

They may be returned once to the recommended ultracold condition, but total cumulative time of storage between minus 25 C to minus 15 C "should be tracked and should not exceed two weeks," the FDA added.

For actual use, the vaccines are thawed and can be stored for up to five days at standard refrigerator temperature, between 2 C and 8 C. The vaccine can then be mixed with saline diluent and should be administered within six hours, during which doses can be stored at refrigerator or room temperature.

The FDA granted an emergency use authorization for the Pfizer vaccine in December.