GSK's RSV Vaccine: Navigating Regulatory Crossroads to Seize Market Opportunity

The race to dominate the respiratory syncytial virus (RSV) vaccine market has intensified, with GlaxoSmithKline (GSK) at a pivotal juncture. While its lead product, Arexvy, faces near-term headwinds from restrictive guidelines and weak sales, its strategic moves to expand approvals in Europe, Japan, and for high-risk populations could unlock a $10 billion-plus market. This article dissects GSK's regulatory progress, competitive dynamics, and the critical factors that will determine whether Arexvy becomes a durable growth driver or a fleeting opportunity.

Regulatory Advances Amid a Crowded Field

GSK's Arexvy has already secured expanded use in the U.S. for adults aged 50–59 at increased risk of severe RSV, leveraging Phase III data showing comparable immune responses to those in older adults. Yet, the vaccine's sales stumbled in early 2025, dropping 57% year-over-year to £78 million. This decline stems from the U.S. Advisory Committee on Immunization Practices (ACIP)'s June 2024 recommendations, which limited Arexvy's use to adults 75+ and high-risk individuals aged 60–74—a narrower scope than initially hoped.

The company is now pushing to broaden its footprint. In Europe, the European Medicines Agency (EMA) has accepted GSK's application to expand Arexvy's use to adults as young as 18, pending approval by mid-2026. Similarly, Japan's regulatory submission remains under review. These moves aim to counter rivals like Pfizer (PFE) and Moderna (MRNA), which already hold approvals for their RSV vaccines in younger high-risk groups.

Market Opportunity: High-Risk Populations and Geographical Expansion

The U.S. alone sees ~42,000 annual hospitalizations among adults aged 50–64 with chronic conditions such as COPD, asthma, or diabetes. Globally, GSK estimates that ~15 million adults in the U.S. and ~30 million in Europe qualify for its expanded indications. However, ACIP's reluctance to recommend Arexvy for adults under 60—due to lingering questions about long-term efficacy and cost-effectiveness—remains a hurdle.

A breakthrough could come from ongoing trials in immunocompromised adults. A Phase IIb trial showed that two doses of Arexvy in kidney/lung transplant patients generated immune responses comparable to healthy older adults. If approved, this could open a new niche for GSK, as no RSV vaccine is currently recommended for such groups under age 60.

Competitive Landscape: A Three-Way Battle

Pfizer's Abrysvo and Moderna's mResvia are GSK's fiercest competitors. Both are approved in the U.S. and EU for adults 60+ and high-risk individuals as young as 18. Pfizer's edge lies in its approval for pregnant individuals to protect infants—a unique use case—but its sales also slumped in early 2025 due to ACIP's restrictive stance. Moderna's mResvia, meanwhile, boasts 80% efficacy in the first four months post-vaccination but faces questions about waning immunity beyond a year.

The reveals investor sentiment: GSK's shares rose 20.8% year-to-date in 2025, outperforming Pfizer (-3.2%) and Moderna (-12.5%). This divergence suggests GSK's diversified pipeline and regulatory momentum are outweighing near-term sales softness.

Risks and Regulatory Uncertainties

The path forward is fraught with risks. First, ACIP's delayed recommendations for adults 50–59 and 18–49 could prolong the sales slump unless the CDC relaxes its stance by late 2025. Second, safety concerns—such as a potential link to Guillain-Barré syndrome (GBS)—could resurface, as the FDA's approval of Pfizer's Abrysvo was accompanied by a warning about rare neurological risks.

In Europe, the EMA's 2026 decision on expanded age indications will be pivotal. A rejection could cede market share to Pfizer and Moderna, which already hold broader approvals in key regions.

Investment Considerations

GSK's stock is trading at a 20.8% YTD gain, reflecting optimism about its long-term RSV prospects. However, investors must weigh near-term execution risks against strategic advantages:

• Buy: If GSK secures EMA approval for adults 18+ in 2026 and ACIP expands recommendations for 50–59-year-olds by late 2025. The stock's Zacks Rank of #2 (Buy) signals consensus on this trajectory.
• Hold: Until regulatory clarity emerges. The RSV market's growth hinges on broadening indications and overcoming ACIP's cautious approach.
• Sell: If real-world data exposes safety flaws or competitors steal market share through faster approvals.

Conclusion

GSK's Arexvy is a testament to the promise—and perils—of adult vaccines. With a first-mover advantage in key age groups and ongoing trials targeting underserved populations, the vaccine could yet become a cornerstone of respiratory disease prevention. Yet, success hinges on navigating regulatory crossroads with precision. Investors should monitor ACIP's fall 2025 meeting and the EMA's 2026 decision closely. For now, GSK's stock reflects a market betting on its resilience—but the final payoff remains contingent on execution in the next 18 months.