Pfizer and BioNTech have agreed to supply their Covid-19 vaccine to the World Health Organisation co-led Covax vaccine access scheme, two sources familiar with the deal said, the latest in a series of shots to be included in the project aimed at lower-income countries.

The deal is expected to be announced on Friday, according to the sources, who declined to be named due to the confidentiality of the agreement.

Details on the size of the deal or the price per dose Covax would pay were not immediately clear, but the sources said the allotment would likely be relatively small. One source said the reason for the limited volume was that the doses were primarily meant for healthcare workers in the countries that Covax serves.

BioNTech declined to comment while Pfizer did not respond to requests for comment. Spokespeople for the WHO and the GAVI vaccine alliance, which co-leads the Covax scheme, also declined to comment.