The global COVAX program, which has relied heavily on AstraZeneca vaccines, announced on Monday that it had reached an agreement to purchase 500 million doses of COVID-19 from Moderna.

The doses will expand the vaccine portfolio under COVAX, which aims to guarantee poor countries equitable access to vaccines to fight the pandemic. Moderna is expected to start supplying the vaccines in the last quarter of 2021, with 34 million doses available before the end of the year, program co-leader Gavi said in a statement.