Moderna Inc said on Wednesday the US government had agreed to increase the contract for the company's COVID-19 vaccine by $236 million to roughly $1.25 billion, to include additional costs related to the shot's studies.

The company and the Biomedical Advanced Research and Development Authority (BARDA) had initially signed a $483 million deal for the vaccine in July last year, which was later increased to about $1 billion.

As of March 31, 2021, the remaining available funding net of revenue earned under the BARDA Contract, prior to the increased payment, was $317 million, Moderna said in a regulatory filing.

The US government in August last year had also separately signed a $1.53 billion deal for 100 million doses of the Moderna vaccine, with an option to buy 400 million more doses.

Moderna's two-dose vaccine is one of the three COVID-19 vaccines authorized for use in the United States. Nearly 30%, or 96.7 million Americans have been fully vaccinated as of April 27, according to data from the US Centers for Disease Control and Prevention.