Pfizer Inc and BioNTech SE have asked the US 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 the 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...