(Bloomberg) -- Moderna Inc. said the U.S. government would buy 200 million more doses of its Covid 19 vaccine in a deal that included the potential for buying other Covid candidates in testing, including booster shots.

The new doses bring the total amount of Moderna vaccine ordered by the U.S. government to 500 million doses, of which 217 million doses had already been delivered as of June 14, the company said in a statement Wednesday. Of the new doses, 110 million will be delivered in the fourth quarter of 2021 and the rest will be delivered in the first quarter of next year, Moderna said.

The deal isn’t entirely a surprise as the original supply deal struck with the U.S. government in August 2020 included options to bring the total order to 500 million doses. Prior to the latest deal, the U.S. had already exercised two of the options to bring its total order to 300 million doses.

“We appreciate the collaboration with the U.S government for these additional doses of the Moderna COVID-19 vaccine, which could be used for primary vaccination, including of children, or possibly as a booster if that becomes necessary to continue to defeat the pandemic,” said Stéphane Bancel, Moderna’s chief executive officer, in the statement.

Moderna did not disclose details of the deal in its release, and a spokeswoman did not immediately reply to a request for comment.

Moderna is testing several potential booster shots in human trials, including one that uses a lower dose of its existing shot and another that combines its existing shot with a messenger RNA vaccine customized against the beta strain first spotted in South Africa.

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