The Covax global vaccine equity programme said Monday it has struck a deal to buy 500 million doses of Moderna's Covid-19 jabs.
The doses, to come on stream from October at the earliest, will broaden out the portfolio of vaccines in the Covax scheme, which has so far been heavily reliant on the AstraZeneca vaccine and hit by delays.
The Moderna doses are expected to start supplying Covax in the final quarter of 2021, with 34 million doses available before the end of the year, the Covax scheme's co-leader Gavi announced in a statement.
A further 466 million doses will follow in 2022.
The Covax facility ensures access to jabs in poor countries, with the cost covered by donors. Wealthier countries can bulk-buy through the scheme.
Covax is co-led by the World Health Organization, the Gavi vaccine alliance and the Coalition for Epidemic Preparedness Innovations.
The scheme aims to distribute enough doses to vaccinate up to 27 percent of the population in the 92 poorest territories participating in the program by the end of the year.
"We are very pleased to sign this new agreement with Moderna, giving Covax facility participants access to yet another highly efficacious vaccine," said Gavi chief executive Seth Berkley.
"Expanding and having a diverse portfolio has always been a core goal for Covax, and to remain adaptable in the face of this continually evolving pandemic -- including the rising threat posed by new variants. This agreement is a further step in that direction."
The agreement also contains options for potential future access to Moderna vaccines that have been adapted to variants of the virus.
For vaccines to be eligible for the Covax programme, they must be authorised by the WHO.
The UN health agency signed off on the Moderna vaccine on Friday.
Covax has so far shipped more than 49 million Covid-19 vaccines globally.
The Moderna jab is already in use in 46 territories around the world, according to an AFP count.
Welcoming the Covax agreement, Moderna chief executive Stephane Bancel said: "This is an important milestone as we work to ensure that people around the world have access to our Covid-19 vaccine.
"We recognise that many countries have limited resources to access Covid-19 vaccines.
"We support Covax's mission to ensure broad, affordable and equitable access to Covid-19 vaccines and we remain committed to doing everything that we can to ending this ongoing pandemic with our mRNA Covid-19 vaccine."