President Donald Trump's administration Wednesday canceled a $590 million contract with Moderna to develop an avian flu vaccine, the U.S. biotech company said.

It marked the latest move against vaccines by Health Secretary Robert F. Kennedy Jr, who has spent decades promoting misinformation about immunization.

The contract, announced Jan. 17 – three days before Trump took office – was for an mRNA vaccine targeting the H5N1 influenza strain, which has been circulating in birds and cattle.

Experts have warned the virus could jump to humans and spark a pandemic.

American pharmaceutical and biotechnology company Moderna disclosed the news as it announced positive results from an early stage clinical trial of 300 people designed to test safety and immune response.

"While the termination of funding from HHS adds uncertainty, we are pleased by the robust immune response and safety profile observed in this interim analysis of the Phase 1/2 study of our H5 avian flu vaccine and we will explore alternative paths forward for the program," said CEO Stephane Bancel in a statement.

"These clinical data in pandemic influenza underscore the critical role mRNA technology has played as a countermeasure to emerging health threats."

The statement added Moderna would "explore alternatives" for funding the development and manufacturing of the vaccine.

Dr. Ashish Jha, a public health expert who served as former president Joe Biden's Covid-19 response coordinator, reacted with dismay.

"The attack on mRNA vaccines is beyond absurd," he posted on X. "It was President Trump's Operation Warp Speed that gave us mRNA vaccines."