HHS cancels $776 million contract for H5N1 mRNA vaccine

A $776 million federal contract to develop an mRNA-based vaccine for H5N1 avian influenza has been abruptly canceled by the U.S. Department of Health and Human Services, citing what it called under-tested technology and unresolved safety issues.

“After a rigorous review, we concluded that continued investment in Moderna’s H5N1 mRNA vaccine was not scientifically or ethically justifiable,” HHS Communications Director Andrew Nixon said in a statement. “This is not simply about efficacy — it’s about safety, integrity and trust.”

The canceled program was part of a pandemic preparedness effort that aimed to adapt mRNA technology — pioneered during the COVID-19 crisis — for zoonotic influenza strains with the potential to spill over to humans.

Moderna, which had received the funding in July 2024, had recently reported positive interim results from a Phase 1/2 clinical study involving 300 healthy adults. The study showed a “robust immune response and favorable safety profile,” according to CEO Stéphane Bancel.

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

Despite these findings, HHS criticized the technology’s “under-tested” nature and expressed a broader intention to redirect vaccine funding toward platforms with longer track records and greater public confidence.

According to the Centers for Disease Control and Prevention, the H5N1 virus has now spread to more than 1,000 U.S. dairy herds and infected over 173 million poultry. While only 70 human cases have been documented in the U.S., global experts remain concerned about the virus’s potential to mutate and cause a human pandemic.

Though Moderna may pursue alternate funding or development avenues, the federal government’s decision may suggest a shift in its pandemic response strategy — and its confidence in mRNA technology. Meanwhile, three other avian flu vaccine candidates remain under development through the National Prepandemic Influenza Vaccine Stockpile.