FRANKFURT (REUTERS) - Pfizer and BioNTech have asked the United States health regulator to relax requirements for their Covid-19 vaccine to be stored at ultra-low temperatures, potentially allowing it to be kept in pharmacy freezers.

Approval by the Food and Drug Administration (FDA) could send a strong signal to other regulators around the world that may ease distribution of the shot in lower-income countries.

The companies have submitted new temperature data to the FDA to support an update to the current label that would allow vials to be stored at -25 deg C to -15 deg C for a total of two weeks.

The current label requires the vaccine to be stored at temperatures between -80 deg C and -60 deg C, meaning it has to be shipped in specially designed containers.

The shot's cold-storage requirements set off a scramble among US states at the beginning of the roll-out for dry ice, in which it can be stored temporarily when there are no specialized freezers available, for instance, in rural areas.

Dr Amesh Adalja, senior scholar at the Johns Hopkins Center for Health Security, said the higher temperatures should "greatly expand the ability to use this vaccine in many parts of the world (or even the US) that do not have the capacity for deep freeze storage".

Pfizer/BioNTech's vaccine, along with Moderna's two-dose shot, has already won US emergency-use authorisation and is being widely distributed as part of the country's mass vaccination efforts.

The FDA confirmed that it had received Pfizer's request and said changes to the vaccine's authorisation must be requested by a company and include data supporting the change. It said authorisation would come either through a granting letter or a reissued letter of authorisation, either of which would be posted on the regulator's website.

The update from the drugmakers comes as two studies from Israel found that the vaccine greatly reduced virus transmission, and the shot was backed by two of the South African government's top advisers.

The new data will also be submitted to global regulatory agencies within the next few weeks, the two companies said.

A BioNTech spokesman declined to provide more details on the timing and which agencies would be contacted.

"The data submitted may facilitate the handling of our vaccine in pharmacies and provide vaccination centres an even greater flexibility," BioNTech chief executive Ugur Sahin said.

Deutsche Post, which has shipped Covid-19 vaccines to several European countries, Israel, Bahrain, Mexico and Singapore, among other states, said -25 deg C would provide some relief but transportation would still not be easy.

A spokesman said air freight would likely no longer require dry ice on board, increasing storage capacity per plane.

BioNTech has said it imposed long-term storage and transportation requirements of -70 deg C out of caution because it had started stability and durability tests on its vaccine relatively late.

Even though it launched its Covid-19 vaccine development programme as early as January 2020, working on four compounds in parallel, it did not decide until July which of the four to proceed with, and only then started stability tests.

If approved, the less onerous storage requirements would provide significant logistical relief.

The World Health Organisation's (WHO) Covax global vaccine-sharing programme has so far limited distribution of Pfizer-BioNTech vaccines to just a few countries, partly out of concern over a lack of infrastructure in developing nations.

The WHO said it was hopeful that eased requirements could broaden its reach.

"We are aware of reports of this and look forward to seeing the data. If proven correct, this could make roll-out of the vaccine easier in all countries, and particularly in low-income ones," it said.

Moderna's product, which like Pfizer's is based on so-called messenger RNA molecules, is already cleared.