[Vaccine. Photo Credit to RawPixel]

On August 5, 2026, the U.S. Food and Drug Administration (FDA) approved Moderna’s mFlusiva (mRNA-1010), the first mRNA-based vaccine for seasonal influenza, for adults aged 50 and older.

However, the approval was not uniform across all age groups.

The vaccine received traditional approval for adults aged 50 to 64, while it received accelerated approval for adults aged 65 and older.

The difference reflects the type of clinical evidence available for the two age groups, with traditional approval for adults aged 50 to 65 based primarily on clinical efficacy data and accelerated approval for adults aged 65 and older based primarily on immune-response data considered reasonably likely to predict clinical benefit.

The FDA’s decision was supported by a Phase 3 clinical trial, known as Study P304, in which 40,805 adults aged 50 and older were randomly assigned to receive either mFlusiva or a licensed standard-dose conventional flu vaccine during the 2024–2025 influenza season.

The trial compared mFlusiva with a conventional flu vaccine.

Results showed that approximately 2.0% of participants who received mFlusiva developed influenza, compared with 2.8% of those who received the standard vaccine.

This translate to a 26.6% relative vaccine efficacy for mFlusiva

 Among participants aged 65 and older, the relative vaccine efficacy was 27.4%.

Common side effects of mFlusiva included injection-site pain, headache and fatigue, but were generally mild or moderate and temporary.

Messenger RNA, commonly known as mRNA, is a molecule that carries instructions from DNA to the cell’s protein-making machinery.

An mRNA vaccine leverages this natural process to train the immune system without introducing the entire virus into the body.

The vaccine delivers laboratory-made mRNA packaged inside lipid nanoparticles that help it enter cells.

The cells briefly use these instructions to make a harmless viral protein, which the immune system recognizes as foreign.

The immune system then produces antibodies and other defenses that can respond more quickly if the actual virus appears.

The mRNA is eventually broken down and does not enter the cell nucleus or alter DNA.

The most well-known examples are Pfizer-BioNTech’s Comirnaty and Moderna’s Spikevax, both used against COVID-19.

While mRNA vaccines had already been approved for COVID-19, no mRNA vaccine for seasonal influenza had previously received FDA approval.

The difficulty was not simply that regulators rejected mRNA technology.

Flu presents a particular challenge because influenza viruses evolve frequently, especially the hemagglutinin (HA) protein targeted by many vaccines.

Traditional flu vaccine production is a lengthy process taking months, creating a risk that the selected strains will not perfectly match those circulating during the season.

Earlier mRNA flu candidates also needed to demonstrate convincing clinical efficacy and safety compared with established vaccines.

Moderna’s  approval journey was not straightforward.

In February 2026, the FDA initially declined to review the company’s application. 

According to Nature Biotechnology, regulators stated that the submission did not contain an adequate, well-controlled study and that its comparator did not represent the best available standard of care.

In response, Moderna subsequently met with the FDA and proposed a revised regulatory approach seeking traditional approval for adults aged 50 to 64 and accelerated approval for adults aged 65 and older.

This regulatory process was important because it allowed Moderna to address the FDA’s concerns over the type of comparator used in older adults while using the available clinical efficacy and immune-response evidence to support separate approval pathways for the two age groups.

For the pharmaceutical industry, mFlusiva demonstrates that the mRNA platform can potentially be adapted rapidly when the genetic sequence of a virus changes.

Moderna’s achievement is the culmination of years of investment in mRNA research, lipid-nanoparticle delivery, manufacturing and large clinical trials.

The technology could eventually support faster updates to seasonal flu vaccines and, with further research, vaccines targeting more influenza strains or conserved viral proteins could provide broader protection.

Researchers are also exploring the use of mRNA technology for diseases beyond influenza, including cancer and other infections.

Moderna is continuing to develop additional mRNA products, while the wider pharmaceutical industry is exploring multivalent, self-amplifying, and other RNA technologies.

Nevertheless, all future vaccines will still need to prove their safety, effectiveness, manufacturing reliability and value through rigorous clinical and regulatory testing.