The US Food and Drug Administration has refused to accept an application from Moderna to review its first mRNA seasonal flu vaccine, the company said on Tuesday, in another blow to the technology that has been the target of some Trump administration health officials.
The agency told Moderna that its application did not contain an “adequate and well-controlled” trial because the control arm did not reflect “the best standard of care available in the United States at the time of the study,” according to a letter dated Feb. 3 that Moderna posted online. It has not identified any safety or efficacy concerns, the company said.
Moderna said that the rejection was inconsistent with previous feedback from the agency and that it had requested a meeting with FDA officials to understand how to proceed.
“The complete stunner here at no point in any of this said it was inadequate” to conduct his clinical trial in the way he discussed with the agency, Moderna’s president, Dr. Stephen Hoge, told CNN on Tuesday.
The US Department of Health and Human Services said that “FDA generally does not comment on regulatory communications to individual sponsors.”
Moderna used a standard-dose seasonal flu vaccine called Fluarix as a comparator in a 40,700-person clinical trial to demonstrate the safety and efficacy of the experimental mRNA vaccine. The company said the FDA had agreed to that plan in April 2024 but suggested it also include data comparing its vaccine to an approved high-dose flu vaccine for people over 65, which the company said it did.
Moderna added that as recently as August, in a meeting before submitting its application for approval of the vaccine, the FDA suggested that it review the submission and assess issues with the comparator during that process. The agency noted that there could be a “significant issue” with the data “during the review” of the application, according to written feedback that Moderna shared.
But last week, the agency refused to do the review altogether, according to the letter. It was signed by Dr. Vinay Prasad, director of the FDA’s Center for Biologics Evaluation and Research, which oversees vaccine regulation.
Prasad was an outspoken critic of the government’s response to Covid-19 before he was appointed to the FDA under HHS Secretary Robert F. Kennedy Jr. He claimed late last year without providing details that Covid-19 vaccines had resulted in the deaths of 10 children and said the agency would change its vaccine approval process.
Moderna is one of three manufacturers in the United States of approved vaccines against Covid-19, along with Pfizer and Novavax. Moderna’s and Pfizer’s vaccines use mRNA technology. Pfizer also has mRNA-based flu vaccines in development.
Although the development at record speed of mRNA-based Covid-19 vaccines during the pandemic was a major achievement of Trump’s first term, his second administration withdrew support for mRNA technology in infectious diseases. HHS canceled 22 projects worth about $500 million focused on the development of mRNA vaccines in August, arguing against evidence that “these vaccines fail to effectively protect against upper respiratory infections such as COVID and influenza.”
The Covid-19 vaccines are estimated to have saved millions of lives. The hope behind applying mRNA technology to seasonal flu vaccines is that it can improve how well they work, allow tailoring to geographic regions where different strains are circulating and lead to combinations with Covid-19 vaccines so that people only need one shot for protection against both viruses.
With the currently approved technology, experts select flu strains for seasonal vaccines each fall during the previous February. Hoge pointed out that mRNA vaccines can be manufactured much more quickly; for the Covid-19 vaccines, he said, the design is decided in May or June, for shipping by August.
Selecting the strains closer to the start of the flu season could potentially lead to a better match with circulating viruses, “and a better match equals, generally, better protection,” Hoge said.
Moderna’s phase 3 study showed in results reported in June that the mRNA-based flu shot produced an efficacy that was about 27% higher than Fluarix in adults 50 and older. A separate trial that assessed safety and immune response included a comparison with a high-dose flu vaccine for people 65 and older and showed superiority, Moderna said.
Immune response is assessed in the laboratory by analyzing blood samples of people who have been vaccinated, while efficacy assessments typically involve seeing how well a vaccine protects against cases of the disease.
Moderna was waiting for the start of the review of its flu shot before moving the experimental flu vaccine and Covid-19 mRNA into the FDA review process, Hoge said. That is now on hold as the company awaits a meeting and further guidance from the agency.
Meanwhile, the combination vaccine is progressing in other countries.
“We expect our first approval to be … probably in Europe, and this year,” Hoge said. “So that will be an important event.”
For more CNN news and newsletters create an account at CNN.com