The Trump administration has delivered its latest blow to vaccines, canceling a nearly $600-million contract to the drugmaker Moderna that was intended to develop a shot for humans against bird flu.

The decision also forfeited the U.S. government’s right to purchase doses ahead of a pandemic, and canceled an agreement set up by the Biden administration in January to prepare the nation for a potential bird flu pandemic. The Moderna contract built on a previous government investment of $175 million last year.

The move was not entirely unexpected. The Department of Health and Human Services said earlier this year that it was reviewing the contract. And Health Secretary Robert F. Kennedy Jr. has repeatedly questioned the safety of mRNA technology, which is used in Moderna’s Covid vaccine.

First used for the Covid vaccines made by Pfizer-BioNTech and Moderna, mRNA shots instruct the body to produce a fragment of the virus, which then sets off the body’s immune response.

Andrew Nixon, a Health and Human Services spokesman, said: “After a rigorous review, we concluded that continued investment in Moderna’s H5N1 mRNA vaccine was not scientifically or ethically justifiable.”

For several years, a type of avian flu known as H5N1 has circulated around the world, killing wild birds and domestic flocks, and spreading to a range of other species including bears and sea mammals.