Washington, Jun 17 (IANS): The US will buy an additional 200 million doses of Moderna's Covid vaccine in anticipation that its citizens may require booster shots, media reports said.

The vaccine doses' delivery is expected to begin this fall and continue till next year and will help the Biden administration to inoculate children under 12, once the US Food and Drug Administration approves, the New York Times reported on Wednesday, citing officials familiar with the plan.

The new doses bring the total amount of Moderna vaccine ordered by the US government to 500 million doses, of which 217 million doses had already been delivered as of June 14, the company said in a statement on Wednesday.

Of the new doses, Moderna expects to deliver 110 million in the fourth quarter of this year, and 90 million in the first quarter of 2022, it said.

"We appreciate the collaboration with the US 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," Moderna CEO Stephane Bancel, said in a statement.

"We remain focused on being proactive as the virus evolves by leveraging the flexibility of our mRNA platform to stay ahead of emerging variants," he said.

Under its existing contract with Moderna, the federal government had until Tuesday to exercise the option to purchase doses for future vaccination needs at the same price it is currently paying -- about $16.50 a dose.

Similar conversations are underway with Pfizer-BioNTech, which also makes a two-dose mRNA vaccine, but no agreement has been reached, one of the officials was quoted as saying to the NYT.