(Reuters) - U.S. health officials are reevaluating a $590 million contract that was awarded to Moderna for the development of its bird flu vaccine, Bloomberg News reported on Wednesday, citing sources.

Shares of the vaccine maker fell 5.5% in after-market trading.

The review is part of a government push to examine spending on messenger RNA-based vaccines, the technology that powered Moderna's Covid vaccine, the report added.

The U.S. government awarded Moderna $590 million in January to advance the development of its bird flu vaccine.

This was in addition to the $176 million awarded by the U.S. Department of Health and Human Services (HHS) last year to complete the late-stage development and testing of a pre-pandemic mRNA-based vaccine against the H5N1 avian influenza.

"While it is crucial that the U.S. Department of Health and Human Services support pandemic preparedness, four years of Biden administration's failed oversight have made it necessary to review agreements for vaccine production," an HHS spokesperson said in an emailed statement, without specifying a review of Moderna's contract.

Last month, Moderna said it was preparing to advance its experimental shot, mRNA-1018, into late-stage trials based on preliminary data from an early-to-mid-stage study and plans to present the data at an upcoming medical meeting.

Moderna did not immediately respond to a Reuters request for comment.

The U.S. will invest up to $1 billion to combat the spread of bird flu, Agriculture Secretary Brooke Rollins said earlier on Wednesday.

A three-year bird flu outbreak in U.S. poultry has killed 166 million chickens since 2022, according to USDA data. The virus has also infected nearly 1,000 dairy herds and almost 70 people, including one who died, since early 2024.

The U.S. Centers for Disease Control and Prevention said on Wednesday that it believes the immediate risk to the general public from H5 bird flu remains low.

The agency added that, to date, person-to-person spread of H5 bird flu has not been identified.