GSK wins FDA approval to extend Arexvy RSV vaccine to at-risk adults aged 18 to 49, opening 21 million-strong US market

GSK plc (NYSE/LSE: GSK), the British pharmaceutical group, has secured US Food and Drug Administration approval to extend the eligible population for its respiratory syncytial virus vaccine Arexvy to adults aged 18 to 49 years carrying at least one risk factor for severe RSV-related lower respiratory tract disease. The expanded label, announced on 13 March 2026, covers conditions including chronic cardiopulmonary disease, kidney disease, obesity, and diabetes. Prior to this decision, Arexvy’s US approval was limited to adults aged 60 and older, and at-risk adults aged 50 to 59. GSK now holds an RSV indication spanning virtually the entire adult population in the United States, a position no rival yet held coming into the 2026 season.

What does the FDA’s expanded Arexvy approval mean for GSK’s RSV vaccine market position in the US?

The practical significance of the approval is best understood in commercial rather than clinical terms. GSK itself estimates that roughly 21 million Americans under the age of 50 carry at least one qualifying risk factor for severe RSV infection, a population the company had been shut out of until now. The annual burden in this cohort includes approximately 17,000 hospitalisations, 277,000 emergency department visits, and just under two million outpatient consultations. That is a substantial addressable base, and it is a cohort that both Pfizer Inc. (NYSE: PFE) with its Abrysvo vaccine and Moderna Inc. (NASDAQ: MRNA) with mRESVIA had been serving commercially since their earlier approvals for adults aged 18 and older at increased risk.

Arexvy’s arrival in this age band thus changes the competitive geometry of the adult RSV vaccine market rather than enlarging GSK’s share of a market it already dominated. Pfizer’s Abrysvo and Moderna’s mRESVIA were already approved for this population, meaning the label gap had been a strategic liability for GSK for the better part of a year. The FDA’s decision closes that gap and allows GSK to compete on equal regulatory footing across the broadest possible adult RSV segment for the first time.

What clinical evidence supported the FDA’s decision to approve Arexvy for younger at-risk adults?

The regulatory filing was anchored to data from a Phase IIIb open-label immunogenicity trial, trial identifier NCT06389487, which enrolled 1,458 participants across 52 locations in six countries including 16 US sites. The trial’s design rested on a non-inferiority framework: the study compared RSV-A and RSV-B neutralisation titres generated in adults aged 18 to 49 at increased risk against those seen in adults aged 60 and above, measured one month after a single dose. The co-primary endpoints were met, with the younger cohort demonstrating immune responses that were not inferior to those of the older reference group.

The safety profile in the 18 to 49 cohort was consistent with findings from the Phase III programme that originally supported Arexvy’s approval in older adults. The most common adverse events were injection-site pain, fatigue, myalgia, headache, and arthralgia, all occurring within four days of vaccination and described as largely transient and mild to moderate. Vaccine efficacy against RSV lower respiratory tract disease was established separately in the original Phase III trial, NCT04886596, and was carried forward to support this supplemental filing. The overall data package was sufficient for a straightforward non-inferiority bridge, which explains the relatively short regulatory timeline from submission acceptance to approval.

How have ACIP recommendation shifts constrained Arexvy’s commercial performance and will this approval change that?

The ACIP backdrop matters as much as the FDA label when assessing Arexvy’s commercial prospects. In June 2024, ACIP narrowed its recommendation for adult RSV vaccination, restricting routine use to adults aged 75 and older and limiting the 60 to 74 cohort to those with elevated risk. That guidance change hit Arexvy sales immediately and heavily. Full year 2024 Arexvy revenue came in at GBP 590 million, more than 50% below the prior year. In the first quarter of 2025, sales fell 57% year-on-year as the ACIP recommendation continued to dampen US market demand. Even as GSK maintained its US market leadership with approximately 55% of older-adult RSV vaccination share in retail pharmacy, the absolute market had contracted sharply.

Recovery began in the second half of 2025. ACIP subsequently issued a positive recommendation for Arexvy’s use in at-risk adults aged 50 to 59, a cohort GSK estimated at around 13 million people. Full year 2025 Arexvy revenue recovered modestly to GBP 600 million, up 2% from 2024, with growth driven principally by European markets including strong uptake in Germany following recommendation and reimbursement, as well as tender deliveries in Spain and Canada. The 18 to 49 approval does not automatically trigger an ACIP recommendation, and that distinction is important. Until ACIP formalises guidance for the 18 to 49 at-risk population, the commercial upside in the US will be constrained by the limits of clinician-initiated shared decision-making rather than a mass-market recommendation pathway.

What competitive pressure does GSK face from Pfizer and Moderna in the newly opened age segment?

Pfizer and Moderna will not yield market share to Arexvy simply because the label gap is now closed. Both companies have had uninterrupted access to the under-50 at-risk population and have been building physician familiarity and payer contracts in that segment. Pfizer’s Abrysvo carried additional differentiation through its maternal immunisation indication, the only RSV vaccine currently approved to protect infants indirectly through maternal vaccination, which underpins a separate commercial channel that Arexvy does not currently address. Moderna’s mRESVIA uses messenger RNA technology and reported strong early-phase efficacy of approximately 80% in the first four months post-vaccination, although durability questions beyond 12 months remain unresolved.

That said, GSK enters the 18 to 49 segment with structural advantages. Arexvy maintained the largest US retail pharmacy market share among RSV vaccines for older adults throughout the 2024 and 2025 seasons despite the ACIP headwind, a function of longstanding pharmacy contracts and brand recognition built since its 2023 approval as the first RSV vaccine for older adults. The AS01E adjuvant system, which is proprietary to GSK, contributes to immunogenicity depth that recombinant protein platforms can claim, distinguishing Arexvy from Moderna’s mRNA-based product at least in the messaging directed at clinicians concerned about durability. Whether those advantages translate into meaningful share in the younger at-risk segment will become clear over the 2026 to 2027 RSV season.

What does GSK’s European approval for Arexvy in all adults 18 and older signal about the global regulatory strategy?

In January 2026, Arexvy received European approval for use in all adults aged 18 and older without an at-risk restriction, a broader label than the FDA has granted. That decision by the European Medicines Agency created a two-tier regulatory reality for GSK: an unrestricted adult indication in Europe and a risk-stratified indication in the US. The contrast has commercial implications because the European approval enables a broader population approach to RSV vaccination campaigns, while the US framework requires clinicians and pharmacies to identify and verify qualifying risk conditions before administering the vaccine.

GSK has indicated it continues to advance regulatory submissions across multiple geographies to expand Arexvy’s availability. The company has approval in 69 markets globally as of year-end 2025, with national RSV vaccination recommendations in place in 21 countries and active reimbursement programmes for Arexvy in nine markets including the United States. The strategic logic is consistent: secure label breadth market by market, then rely on evolving public health guidance and reimbursement frameworks to convert regulatory access into commercial volume. The 18 to 49 FDA approval adds the most commercially important single market to that footprint.

How have GSK shares responded and what does the market reaction imply about the approval’s perceived value?

GSK shares on the NYSE traded in the region of USD 55 at the time of the announcement on 13 March 2026, having recovered substantially over the prior 12 months. The stock has gained approximately 42% over the trailing year, and is trading near the upper end of its 52-week range of approximately USD 32 to USD 62 on the London Stock Exchange, a recovery that reflects the broader rehabilitation of GSK’s investment case following the resolution of Zantac litigation liabilities and a return to earnings growth. Full year 2025 earnings were up more than 100% year-on-year, driven by lower legal charges and strong performance in Specialty Medicines.

The Arexvy approval did not generate an outsized single-day move, which is consistent with the market having partially anticipated the decision following FDA acceptance of the submission and the European label precedent. Analyst sentiment heading into the approval was mixed: Barclays maintained a Sell rating as recently as early March 2026, citing execution uncertainty and competitive dynamics, while Citi held a neutral stance. The market appears to be pricing the 18 to 49 approval as a directionally positive but commercially contingent development, the ultimate value of which depends on whether ACIP broadens its recommendation to the 18 to 49 risk cohort and whether GSK can translate label parity into durable market share in a segment where Pfizer and Moderna had a head start.

Key takeaways on what the Arexvy age expansion means for GSK, its rivals, and the adult RSV vaccine market

• GSK’s Arexvy now holds a US indication spanning adults 18 and older at increased risk, closing the label gap that had allowed Pfizer’s Abrysvo and Moderna’s mRESVIA to serve the under-50 population without competition from the market leader.
• The addressable US population under the new label is estimated at 21 million adults, though commercial conversion depends on whether ACIP issues a formal recommendation for the 18 to 49 at-risk cohort.
• Arexvy’s 2025 full year revenue was GBP 600 million, recovering modestly from the 2024 decline driven by restrictive ACIP guidance, with growth powered by European markets rather than the US.
• The FDA approval was supported by a Phase IIIb non-inferiority immunogenicity bridge trial and did not require new efficacy data; the clinical package was largely a regulatory formality once the immunogenicity comparison was met.
• Pfizer’s Abrysvo retains the maternal immunisation indication, a structurally distinct commercial channel that Arexvy does not contest, providing Pfizer with a revenue buffer independent of adult vaccine competition.
• Moderna’s mRESVIA faces durability questions beyond 12 months post-vaccination, a potential differentiator for protein-based vaccines including Arexvy in clinician conversations about longer-term protection.
• GSK’s European approval covers all adults 18 and older without an at-risk qualifier, positioning Arexvy more aggressively in European markets than in the US and creating asymmetric commercial opportunity across geographies.
• GSK’s NYSE-listed shares have rallied approximately 42% over the past year, trading near the top of the 52-week range, with the Arexvy approval contributing to rather than driving sentiment given partial market anticipation.
• The near-term US commercial impact will be modest without an ACIP recommendation update; the structural significance of the approval is that it removes the regulatory ceiling on Arexvy’s potential population reach in the US’s most important RSV market.
• A revaccination guidance decision from US public health authorities remains a separate open question; positive guidance on booster dosing would materially expand the addressable market across all three RSV vaccine makers simultaneously.