COVAX, the global project to share COVID-19 vaccines, and the African Union have declined options to buy additional doses of Moderna's shot, as developing nations struggle to allocate supplies.
A spokesperson for Gavi, part of the COVAX alliance, confirmed the news.
The discussions with Moderna are part of "regular decision-making process on exercising options outlined in our advance purchase agreements with manufacturers", the spokesperson said.
Moderna and Gavi have agreements for up to 650 million doses of the company's vaccine to be made available to COVAX participants through 2021 and 2022.
COVAX, also backed by the World Health Organization and the Coalition for Epidemic Preparedness Innovations (CEPI), has picked up pace of supplies after struggling to acquire shots last year.
It has delivered about 1.40 billion doses to 144 countries as of April 1.
As supply and donations ramped up, some poorer nations are facing hurdles such as gaps in cold-chain shortage, vaccine hesitancy and a lack of funds to support distribution networks.
"We are in conversations with manufacturers ... to align with magnitude and timing of country needs," the Gavi spokesperson added.
The news was first reported by Bloomberg News.