26.6 percent. That is the relative efficacy edge Moderna's mRNA flu shot showed over a licensed standard-dose vaccine in its pivotal trial. On August 5, the FDA decides whether that is enough to make it the first seasonal mRNA influenza vaccine on the market.
The vaccine beat a standard-dose shot by 26.6% on relative efficacy overall. In adults 65 and older the edge was 27.4%, from a trial of 40,805 people across 11 countries.
Approval would reset the flu vaccine business. Egg-based manufacturing, supply lead times, and strain-matching accuracy are all suddenly open questions.
Flu vaccine production has worked the same way for seventy years. Grow the virus in eggs, inactivate it, formulate, ship. It works. It is also slow, fragile to strain drift, and hostage to a supply chain that must commit to strains months before the season.
mRNA-1010 relative vaccine efficacy
Pivotal Phase 3 trial P304 enrolled 40,805 adults across 11 countries, comparing a single mRNA-1010 dose to a licensed standard-dose flu shot. · VRBPAC briefing document, 2026
The road from refusal to a 9-0 vote
The path here was not smooth. In February, the FDA refused to file Moderna's application. The Refusal-to-File letter centered on the comparator chosen in the trial: a standard-dose vaccine rather than the high-dose or adjuvanted formulations typically preferred for older adults. Moderna worked through a Type A meeting, revised the submission, and the agency accepted it with a PDUFA date of August 5.
The regulatory design that emerged is layered. For adults 50 to 64, Moderna seeks traditional approval, supported by clinical efficacy data. For those 65 and older, the group that carries the bulk of flu mortality, the company seeks accelerated approval, backed by safety, immunogenicity, and relative efficacy data, plus a post-marketing confirmatory study. It is a pragmatic structure. Get the product out before the 2026-2027 season, then prove the hardest claim later.
The advisory committee's June vote was unambiguous. Both questions ended 9-0 in favor, with the panel concluding the benefits outweighed the risks. Advisory votes are non-binding, but the agency follows them far more often than not.
What the data actually shows
Relative efficacy of 26.6% means the mRNA vaccine prevented 26.6% more influenza-like illness than a standard-dose comparator. The strain-level breakdown matters for how real this is: 29.6% against A/H1N1, 22.2% against A/H3N2, 29.1% against B/Victoria lineage. This is not a single-strain fluke. The signal is distributed across the main circulating subtypes.
The 65-and-older subgroup reported 27.4% rVE, roughly matching the overall population. That is the number that matters most commercially. Older adults are where flu does its damage, where high-dose and adjuvanted vaccines have carved out premium pricing, and where the CDC tracked a 2024-2025 season with over 600,000 hospitalizations.
We believe mRNA-1010 has the potential to provide an important new option for seasonal flu prevention and further demonstrate the versatility of our mRNA platform.— Stéphane Bancel, CEO, Moderna
The trade-off is on safety. Solicited adverse reactions within seven days were more frequent with mRNA-1010 than with the comparator: injection-site pain, fatigue, headache. The committee weighed this against the efficacy edge and found the balance acceptable. In the 65+ population, where an approval decision must rest on a narrower accelerated-approval base, this reactogenicity profile is the main open question.
| Parameter | mRNA-1010 | Standard-dose shot |
|---|---|---|
| Manufacturing | ✔ cell-free, weeks | ✗ egg-based, months |
| Strain matching | ✔ precise, late selection | ◐ commit months ahead |
| Relative efficacy | ✔ +26.6% | ◐ baseline |
| Reactogenicity | ◐ higher short-term | ✔ milder |
The business case is not the usual one
Here is where this story differs from a typical approval play. Moderna is not modeling revenue from mRNA-1010 in 2026. The company has said an August approval is late in the flu planning cycle, and it cites the mRESVIA experience: an RSV vaccine approved mid-year in 2024 that generated just $25 million in its first full year, burned by competition and the timing of the season.
That honesty matters for anyone reading the decision day as a binary stock event. Historical data on large-cap PDUFA decisions shows a median one-day stock move around 1%. The approval itself is only the beginning of a commercial story that runs through the 2027-2028 season, distribution agreements, ACIP recommendation, and physician adoption.
The real prize is platform proof. Flu is a far larger market than RSV. Moderna's CFO has sized the European flu vaccine market at about $1 billion in 2027, against $100 million for RSV. A flu approval would validate the mRNA platform's second major commercial application and set up the combination vaccines, the COVID/flu shot already authorized in Europe as mCOMBRIAX, that are the actual endgame.
What happens to the market a year from now?
Probability: 70% — mid-year approval, conservative company guidance, and the lead time to win ACIP recommendation and distribution slot all push volume to the second season.
✅ Arguments for
Efficacy edge holds across the main circulating strains and in the 65+ subgroup.
EU, Canada, and Australia are reviewing in parallel; EU combination vaccine already authorized.
Confirmation criteria: FDA follows the committee; ACIP recommendation lands before the 2027 season.
❌ Arguments against
Reactogenicity is higher; uptake among a vaccine-skeptical older population is unproven.
A mid-year approval repeats the mRESVIA timing failure; incumbents lock seasonal supply early.
Disconfirmation criteria: FDA delays or conditions the 65+ approval; ACIP defers; first-season volume stays near zero.
Development scenarios
🟢 Optimistic scenario (30%)
Implications: flu becomes a recurring seasonal revenue line and Moderna's commercial floor stops depending on COVID alone.
🟡 Base-case scenario (55%)
Implications: modest 2026 contribution, rising revenue through 2027, and a working proof point for the mRNA platform beyond COVID.
🔴 Pessimistic scenario (15%)
Implications: the platform story stays one approval behind; competitors' mRNA flu programs gain ground in the interim.
The August 5 FDA decision itself and whether both age bands are approved as proposed.
ACIP recommendation and the timing of distribution agreements for the 2027 season.
Enrollment and interim readouts of the post-marketing confirmatory study in adults 65+.
US regulatory progress of the mCOMBRIAX combination vaccine, already authorized in Europe.
