Moderna Rises 6% Despite GSK Moving Rival mRNA Flu Vaccine to Phase III

Moderna Rises 6% Despite GSK Moving Rival mRNA Flu Vaccine to Phase III

David Moadel

Tue, September 1, 2026 at 9:00 PM GMT+3 5 min read

Quick Read

• MRNA climbed 6% as traders read GSK's Phase III mRNA flu commitment as platform validation rather than a competitive threat to mFlusvia.

• Moderna's Phase III melanoma win with MRK as co-developer rekindled platform interest, and BNTX also carries read-through as mRNA's commercial standing deepens.

• Jefferies analyst Andrew Tsai cautioned investors won't rush into mRNA therapies without demonstrated success across a broad range of solid tumors.

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Today's major mRNA headline is a competitive threat to Moderna (NASDAQ:MRNA), and the stock is climbing anyway. That tension is the story on the tape, and it's worth reading as a platform bet rather than a flu vaccine call. This MRNA stock rally sits inside a much larger year-to-date advance, so the reaction function matters more than the magnitude.

Moderna stock is up 6% to $148.32 midday, extending a run that had the stock up 376% year to date through Monday's close. Behind the move is a rival program from GSK (NYSE:GSK), with GSK stock up 0.7% to $50.60. No Moderna release accompanied the move.

The iShares Biotechnology ETF (NASDAQ:IBB) is up 0.3% to $209.70. Meanwhile, the SPDR S&P 500 ETF Trust (NYSEARCA:SPY) is down 0.7% to $761.68. Biotechnology is modestly outperforming a falling broad market, and Moderna is far above both, which places this move in the name rather than the sector.

GSK Moves a Rival mRNA Flu Shot to Phase III

GSK stated it will advance its seasonal mRNA-based influenza vaccine into a Phase III trial after positive mid-stage results, and hopes to begin that trial in September 2026. In the Phase IIa Flu-028 study, 971 adult volunteers were randomised, and recipients of the multivalent candidate showed higher immune responses than those given marketed standard-dose and high-dose comparators, with what the company called an acceptable safety and short-term inflammatory profile.

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Results were presented at the OPTIONS XIII influenza conference in Washington, DC. The company is advancing an optimised B-strain haemagglutinin form, and the study would be the first late-stage evaluation of an mRNA flu vaccine targeting both haemagglutinin and neuraminidase. Sanjay Gurunathan is GSK's head of vaccines and infectious disease research and development.

Moderna's mFlusvia, its mRNA seasonal flu shot, won U.S. Food and Drug Administration approval in August 2026, after the agency initially declined to review it at all. GlobalData forecasts mFlusvia sales of $831 million in 2032. A rival candidate reaching market would compete with mFlusvia directly.

Platform Read-Through Versus Direct Competition

One tape reading is that a large, conservative pharma company is committing capital to the exact modality that U.S. policy defunded last year. U.S. Health Secretary Robert F. Kennedy Jr. cut government funding to 22 mRNA vaccine development initiatives worth $500 million in August 2025. Private financing for the modality fell 82% in 2025 against 2023 levels.

Moderna's Phase III melanoma success for intismeran autogene, its mRNA cancer vaccine, reopened analyst interest in the platform after months of skepticism. Merck (NYSE:MRK) is a co-developer on that program and holds significant economic rights to the therapy. That trial used Keytruda as the comparator arm, and the data pointed to additive efficacy over Merck's Keytruda alone in the adjuvant setting, which surprised much of the sell side.

This platform question also reads across to BioNTech SE (NASDAQ:BNTX) as another mRNA developer with commercial infrastructure in place. GSK's decision to fund a late-stage mRNA flu program, in that context, looks to some traders like third-party validation of the modality itself. The market appears to be paying for that read-through rather than pricing the future revenue GSK might take from mFlusvia.

Bear Case Deserves Real Weight

Jefferies senior equity research analyst Andrew Tsai stated that investors were unlikely to rush back into mRNA therapies, with longer-term interest hinging on whether the drug class succeeds across a broad range of solid tumors. That framing puts a ceiling on how far one Phase III entrant from a large pharma company can carry a re-rating in the near term.

Pair that view with the fact that MRNA stock's 376% year-to-date run means a 6% session is now ordinary volatility for Moderna stock rather than a signal. The stock has moved much more than that on individual data releases this summer, and single-session activity carries less signal at these price levels than it did in prior years.

What to Watch Next

A core question is whether competitive validation of a platform is worth more to Moderna than the revenue a competitor would take from mFlusvia. Both readings are defensible on today's information, and the market has picked the platform read for now. Fresh trial data or a slowdown in the pace of mFlusvia's launch could shift that balance quickly.

Investors can watch for whether Moderna stock holds its gains and how sell-side analysts frame the GSK study details in follow-up notes. Given the size of the year-to-date advance, traders should consider keeping their position sizes modest and treating single-session moves as noise rather than confirmation.

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