Moderna is expected to start supplying Covax in the final quarter of 2021, with 34 million doses available before the end of the year.
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 Global Alliance for Vaccines and Immunisation (Gavi), and the Coalition for Epidemic Preparedness Innovations.
The scheme aims to distribute sufficient doses to vaccinate up to 27 percent of the population in the 92 poorest territories participating in the programme 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.
COVAX gets boost from Moderna deal, Sweden's donation of COVID-19 vaccines -GAVI https://t.co/QSgV7xna8H pic.twitter.com/7CTSZTNwH9
— Reuters (@Reuters) May 3, 2021
"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 last Friday.
Forty-nine million doses administered
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.
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 just announced an agreement with Gavi, the Vaccine Alliance to supply up to 500 million doses of the COVID-19 Vaccine Moderna, including an initial 34 million doses to be delivered in the fourth quarter of 2021. Read more: https://t.co/pTvAIqsRJr pic.twitter.com/nxglzgfEXN
— Moderna (@moderna_tx) May 3, 2021
"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."
The value of the deal has not been made public, but Moderna insists the price offered to Covax is in the company's lowest tier.
