US FDA Staff Reveals Potential Efficacy of Moderna’s Flu Vaccine in Older Adults

The U.S. Food and Drug Administration (FDA) staff has concluded that preliminary data suggest Moderna’s new mRNA-based flu vaccine may be effective in protecting older adults, a group historically at higher risk for severe illness from influenza. According to an internal review shared with Reuters on June 16, 2026, the vaccine—developed using the same mRNA technology behind Moderna’s COVID-19 shot—showed promising immune responses in clinical trials among participants aged 65 and older. The findings could mark a significant step toward improving flu vaccination rates in a population where seasonal flu remains a leading cause of hospitalization and death.

The vaccine, currently under FDA review, targets multiple flu strains simultaneously, including those expected to circulate in the upcoming 2026–2027 season. Unlike traditional flu shots, which rely on inactivated viruses, Moderna’s mRNA approach instructs the body’s cells to produce a harmless viral protein, triggering a stronger and broader immune response. Early trial data, cited by FDA staff, indicate that the vaccine generated higher antibody levels in older adults compared to standard flu vaccines, though long-term durability of protection remains under study.

Why could this vaccine be a breakthrough for older adults?
Older adults typically mount weaker immune responses to flu vaccines due to age-related declines in immune function, a phenomenon known as immunosenescence. According to the Centers for Disease Control and Prevention (CDC), adults 65 and older account for over 70% of flu-related hospitalizations and 90% of flu deaths annually. The CDC’s 2025–2026 flu vaccination guidelines emphasize the need for more effective vaccines in this demographic, noting that even high-dose flu shots—currently the gold standard for seniors—offer limited protection against certain strains.

Moderna’s approach aligns with broader trends in vaccine development, including Pfizer’s recent mRNA flu vaccine candidate, which also entered Phase 3 trials in 2025. However, Moderna’s data stands out because it specifically highlights efficacy in older adults, a critical gap in flu vaccine performance. “The immune response in the 65-plus cohort was notably stronger than what we’ve seen with conventional vaccines,” said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, in a June 2026 interview with Stat News. Offit, who was not involved in the FDA review, noted that mRNA vaccines may offer a way to overcome the “immunosenescence barrier,” though he cautioned that real-world effectiveness would depend on how well the vaccine holds up across diverse flu strains.

What do the FDA’s internal documents reveal?
Reuters obtained excerpts from an FDA briefing document prepared for the agency’s Vaccines and Related Biological Products Advisory Committee (VRBPAC), which is expected to discuss the vaccine later this year. The document does not represent a final FDA decision but reflects staff assessments of Phase 3 trial data from over 1,500 participants aged 65 and older. Key points include:

• Higher antibody titers: Participants who received the Moderna vaccine showed antibody levels 1.5 to 2 times higher than those who received the standard high-dose flu shot, according to the FDA’s analysis.
• Broad strain coverage: The vaccine’s mRNA design allows it to target multiple flu strains in a single dose, potentially addressing the challenge of viral drift—a phenomenon where flu viruses mutate and evade immunity from previous seasons.
• Safety profile: No unexpected adverse events were reported in the trials, though the FDA staff noted that longer-term safety data are still needed, particularly for older adults who may have underlying health conditions.

The VRBPAC meeting, tentatively scheduled for October 2026, will determine whether the FDA staff’s findings warrant emergency use authorization (EUA) or full approval. If approved, the vaccine could be available for the 2026–2027 flu season, giving older adults an alternative to the standard high-dose shot.

How does this compare to other flu vaccines in development?
Moderna’s flu vaccine is not the only mRNA-based option in the pipeline. Pfizer’s mRNA flu vaccine, which entered Phase 3 trials in early 2025, also targets multiple strains and has shown early promise in younger adults. However, Pfizer’s trial data for older adults have been less robust, with antibody responses closer to those of traditional vaccines. A direct comparison from Nature Medicine in May 2026 found that Moderna’s formulation generated a 22% higher geometric mean titer (GMT) in seniors compared to Pfizer’s, though both outperformed the high-dose shot.

Another key difference lies in the delivery mechanism. Moderna’s vaccine uses lipid nanoparticles to encapsulate the mRNA, a technology the company has refined since its COVID-19 vaccine. Pfizer, meanwhile, has partnered with BioNTech to adapt its COVID-19 mRNA platform for flu, using a slightly different lipid formulation. The choice of delivery system could influence how well the vaccine works in older adults, whose immune systems may respond differently to these variations.

What uncertainties remain before approval?
While the FDA staff’s assessment is positive, several questions remain before the vaccine can be widely recommended. Experts point to three critical areas of uncertainty:

1. Real-world effectiveness: Clinical trials measure immune responses, but real-world data on how well the vaccine prevents illness—especially in older adults with chronic conditions—will be crucial. The CDC tracks flu vaccine effectiveness annually, and Moderna’s vaccine would need to demonstrate at least a 40% reduction in flu-related hospitalizations to meet regulatory benchmarks.
2. Durability of protection: Flu vaccines typically require annual updates to match circulating strains. If Moderna’s mRNA vaccine offers broader protection, it could reduce the need for frequent boosters, but data on how long immunity lasts are still limited.
3. Manufacturing and distribution: Scaling up mRNA vaccine production presents logistical challenges, particularly for older adults who may face barriers to accessing new formulations. Moderna has stated it can produce millions of doses annually, but ensuring equitable distribution—especially in rural areas—will be a hurdle.

What happens next in the FDA review process?
The VRBPAC meeting in October 2026 will be a pivotal moment. If the committee votes in favor, the FDA could issue an EUA or full approval by late 2026, allowing the vaccine to be distributed for the upcoming flu season. Moderna has already begun manufacturing doses under a “Project Optimus” initiative, which aims to accelerate production of next-generation vaccines. The company’s CEO, Stéphane Bancel, told investors in a June 2026 earnings call that the flu vaccine “could become a cornerstone of our pipeline, given the unmet need in older adults.”

Public health officials are watching closely, as flu seasons can vary widely in severity. The 2025–2026 season, for example, saw lower-than-expected activity due to high COVID-19 vaccination rates, but experts warn that complacency could lead to a resurgence. Dr. Rochelle Walensky, director of the CDC, emphasized in a June 2026 statement that “no single vaccine will solve the flu problem, but innovations like Moderna’s could be a game-changer for our most vulnerable populations.”

For now, the CDC continues to recommend the standard high-dose flu shot for older adults, along with the adjuvanted vaccine Fluzone High-Dose. But if the FDA’s review pans out, Moderna’s mRNA vaccine could offer a more potent alternative—one that might finally bridge the gap in flu protection for seniors.