RSV Vaccine Battle: GSK Leads, Moderna Bets, Pfizer Holds

Three vaccines. At least $3 billion in annual revenue and climbing. GSK, Pfizer, and Moderna are fighting over who vaccinates 80 million American adults 60 and older against respiratory syncytial virus. The RSV vaccine market went from zero to $1B+ annual revenue in two years. The question for investors is which stock actually moves on this franchise.

The RSV vaccine total addressable market is substantial. The CDC estimates RSV causes 60,000 to 160,000 hospitalizations and 6,000 to 13,000 deaths annually among older adults in the United States alone. Add maternal vaccination covering 3.7 million annual births for infant protection, and the global opportunity sits at $10 billion at maturity. Industry estimates peg the 2026 market at approximately $1.1 billion, with projections to $3.4 billion by 2034. The U.S. market is expanding rapidly on the back of ACIP recommendations that now cover all adults 75 and older and adults 50 to 74 at increased risk. The 2026-2027 season, which starts in September, is the first where GSK, Pfizer, and Moderna all have labels covering adults 18 to 59 at increased risk.

GSK’s Arexvy was first to market and remains the efficacy leader. The AReSVi-006 Phase 3 trial produced 82.6% efficacy against RSV-LRTD in season one, 56% in season two, and 48% in season three. Cumulative efficacy over three full seasons was 62.9% against RSV-LRTD. No other RSV vaccine has durability data through three full seasons. Arexvy is an adjuvanted protein subunit vaccine, the conventional technology with the longest real-world track record. GSK also expanded Arexvy’s label in March 2026 to younger adults at increased risk, widening the addressable population. GSK at $51.53 and a $103B market cap is a diversified pharma: Arexvy is an important growth driver but does not transform the stock. Revenue from vaccines and infectious disease was a meaningful but not dominant contributor to GSK’s Q2 results. The stock is a Hold on the RSV thesis alone.

Pfizer’s Abrysvo is the maternal immunization champion. The bivalent RSVpreF vaccine is the only RSV shot approved for maternal vaccination at 32 to 36 weeks of gestation, giving Pfizer a monopoly on the infant protection market. In older adults, the RENOIR Phase 3 trial showed 88.9% efficacy in season one and 77.8% in season two, with cumulative two-season efficacy of 81.5%. Both RSV A and B subtypes showed 80% or higher efficacy. That is competitive with Arexvy on two-season data, though Abrysvo lacks the three-season durability evidence GSK has published. Pfizer and GSK collectively hold more than 90% of the U.S. RSV vaccine market. At $25.41 and a $143B market cap, Pfizer is the largest of the three RSV players. The RSV franchise matters for Pfizer as a post-COVID revenue offset, but it is not a thesis-defining catalyst. The maternal monopoly is the most durable competitive moat in the market, but the older-adult segment is a two-horse race with GSK. Pfizer’s stock is a Hold: the RSV franchise supports the base but does not re-rate a $143B market cap.

Moderna’s mRESVIA is the existential bet. The mRNA-1345 vaccine showed 83.7% efficacy against RSV-LRTD with at least two symptoms at a median 3.7 months of follow-up in the ConquerRSV Phase 3 trial, published in the New England Journal of Medicine. Efficacy was 68.4% against RSV-associated acute respiratory disease. These are strong single-season numbers, competitive with GSK and Pfizer’s first-season results. Durability is the unanswered question: Moderna has not yet published multi-season data, and the mRNA platform’s shorter durability in COVID vaccines raises the question of whether mRESVIA protection will wane faster than protein subunit competitors. The FDA expanded mRESVIA’s label to adults 18 to 59 at increased risk in 2026, matching GSK’s expanded label reach. The prefilled syringe format is a genuine convenience advantage versus GSK and Pfizer’s vial-and-syringe presentations. The mRNA manufacturing advantage, however, has not yet translated to market share. GSK and Pfizer together control more than 90% of the RSV vaccine market.

The durability question is the crux of the RSV investment thesis. GSK has three-season data showing protection persists with clinically meaningful efficacy. Pfizer has two-season data. Moderna has less than one. If mRNA durability proves inferior over three to five years, mRESVIA loses the ACIP recommendation battle. ACIP’s updated 2025 guidance recommends a single lifetime dose for adults 75 and older. If Arexvy is the only shot with proven multi-year protection, it captures the majority of the 75-plus market. ACIP has not yet issued a revaccination recommendation for any RSV vaccine, but GSK is actively studying revaccination schedules. The first company to secure an ACIP revaccination recommendation wins the recurring revenue stream.

At $56.99 and a $22B market cap, Moderna’s stock trades on the mRNA platform thesis. mRESVIA is the company’s second approved product after Spikevax. For a company that generated $19 billion in COVID vaccine revenue in 2022 and now projects $2.2 billion in 2026 revenue, every non-COVID approval is existential. Moderna’s pipeline has produced mixed results: the norovirus vaccine Phase 3 interim missed early success criteria in July 2026, and the flu vaccine PDUFA is on the calendar for August 5 but has shown mixed efficacy. The MRNA Q2 earnings report laid out a $2.4 billion operating loss gap and approximately 2.5 years of cash runway. mRESVIA revenue, even at peak, contributes perhaps $500 million to $1 billion annually. That narrows the loss but does not close it. The mRNA platform economics piece is covered elsewhere; for this analysis, what matters is that RSV alone does not save Moderna. It buys optionality.

The risks in the RSV market are structural, not company-specific. First, the FDA added a Guillain-Barré syndrome warning to GSK and Pfizer’s RSV vaccine labels in January 2025. The warning is a class effect that suppresses uptake among vaccine-hesitant populations and gives physicians a reason to defer vaccination. Second, ACIP’s narrowing of the 2025 recommendation from shared clinical decision-making for all adults 60-plus to age-based and risk-based criteria reduced the eligible population by excluding healthy adults 60 to 74. Third, all three vaccines show waning efficacy: Arexvy dropped from 83% season one to 48% season three. If durability is a class-wide problem not solved by any technology, the market’s peak revenue may be lower than current projections. Fourth, Sanofi’s Beyfortus (nirsevimab) is the dominant pediatric RSV prophylaxis and competes indirectly by reducing the disease reservoir that drives adult exposure.

The verdict: GSK is the only RSV vaccine with efficacy data through three full seasons. The stock will not move on Arexvy because GSK at $103B is a diversified pharma where RSV is meaningful but not transformative. Pfizer has the maternal monopoly and competitive older-adult efficacy, but at $143B the RSV franchise is a single-digit percentage of revenue. Pfizer is a Hold. Moderna at $22B has the most asymmetric RSV exposure: mRESVIA success is necessary but not sufficient for the stock to work. The company needs three or four pipeline approvals to offset COVID revenue decline, and RSV is one of them. If mRESVIA multi-season durability data in 2027 proves competitive with Arexvy, the stock gets a catalyst. Until then, MRNA is a Hold. The trade is not which vaccine wins. It is which stock price actually moves on the outcome, and the multi-season durability data in 2027 settles the debate.