The U.S. government is in negotiations with Moderna to potentially secure additional Covid-19 vaccine doses to supply to the world, according to a person familiar.

The discussions may lead to a similar number of doses purchased as a deal revealed Wednesday with Pfizer, said the person, who declined to be named because the negotiations aren't public.

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President Joe Biden is expected to announce at the G-7 summit that the U.S. has bought 500 million doses of the Pfizer-BioNTech vaccine to share through the global Covax alliance for donation to 92 lower-income countries and the African Union over the next year, according to another person familiar. The news was first reported by The Washington Post and The New York Times.

The Pfizer doses will be purchased at a not-for-profit price, the person said. The terms of a potential Moderna deal weren't immediately clear.

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