One week after saying it was refusing to review Moderna’s application for approval of a new flu vaccine, the US Food and Drug Administration’s (FDA’s) Center for Biologics Evaluation and Research (CBER) has reversed course and will review the application for an mRNA flu vaccine for those 50 and older.

Before the initial reversal, the FDA previously indicated support for the company’s phase 3 findings for the vaccine.

In a news release today, Moderna explained it proposed a revised regulatory approach for its investigational seasonal influenza vaccine candidate, mRNA-1010. Moderna is now seeking full FDA approval for adults 50 to 64 years of age and accelerated approval for adults 65 and older, along with a post-marketing requirement to conduct an additional study in older adults.

Moderna said the FDA has accepted the application for review, with a deadline of August 5, 2026.

We look forward to making our flu vaccine available later this year so that America’s seniors have access to a new option to protect themselves against flu.

“We appreciate the FDA’s engagement in a constructive Type A meeting and its agreement to advance our application for review,” said Stephane Bancel, MBA, MEng, Moderna CEO. “Pending FDA approval, we look forward to making our flu vaccine available later this year so that America’s seniors have access to a new option to protect themselves against flu.”

‘We don’t have any idea’ why FDA changed course

The FDA had refused to review the original application because it said Moderna’s phase 3 study was not “adequate and well-controlled.” Most in question was the use of a standard-dose flu shot in the comparator arm of the trial for those 65 and older, instead of a high-dose seasonal flu vaccine. Moderna said CBER had previously approved the study design, and Bancel told the media the FDA had not expressed any concern with the safety or efficacy of mRNA-1010.

The FDA, has, under the leadership of Health and Human Services Secretary Robert F. Kennedy Jr., slashed $500 million in mRNA contracts as of last August. Kennedy has been a longtime opponent of mRNA vaccines, including the vaccines developed against COVID-19 during Operation Warp Speed under President Donald Trump’s first term.

In addition to confusing top Moderna executives, last week’s refusal shook the confidence of the vaccine market. The New York Times said vaccine manufacturers, including Moderna, were cutting jobs and curbing research in the United States to anticipate further anti-vaccine business during this administration.

It’s not clear if external economic pressures caused the FDA to backtrack, however.

“We don’t have any idea why they reversed course,” infectious disease expert Michael Osterholm, PhD, MPH, said when asked about today’s announcement. “That’s part of the problem.”

Osterholm, director of the University of Minnesota’s Center for Infectious Disease Research and Policy, which publishes CIDRAP News, said vaccine developers need consistent policy and protocol. “They need to know what is needed for approval, and how it would be supported after approval. Without that we will see a rapidly changing vaccine landscape.

This current situation demonstrates how out of control we are in the FDA’s consideration and review of currently licensed vaccines and potential new vaccines.

“This current situation demonstrates how out of control we are in the FDA’s consideration and review of currently licensed vaccines and potential new vaccines.”

Robert H. Hopkins Jr., MD, medical director of the National Foundation for Infectious Diseases, said he was hopeful about today’s news, and what it means for mRNA vaccine development.

“It is hard to assess whether this is an indication of changes in agency leadership’s approach to new vaccine applications or not; but I am hopeful that it does,” Hopkins said in a statement to CIDRAP News. “The availability of another option for influenza vaccination, particularly if it is using a technology which allows more rapid changes in the vaccine to adapt to strain changes than is an option with current influenza vaccines, will potentially be a major step forward in efforts to protect the health of individuals from severe influenza.”