Sanofi Discontinues RSV Vaccine for Toddlers Following Phase 3 Setback

Sanofi, the French pharmaceutical giant, has announced the termination of its respiratory syncytial virus (RSV) vaccine program for toddlers after disappointing results in a late-stage clinical trial. The decision marks a significant shift in the company's RSV strategy and highlights the challenges in developing effective vaccines for young children.

Phase 3 Trial Failure Leads to Program Termination

Sanofi's intranasal live attenuated vaccine, known as SP0125, was being evaluated in a phase 3 study involving approximately 6,300 children aged between 6 months and 22 months. The study, which began last year and was scheduled to conclude at the end of 2027, was halted prematurely after an independent data monitoring committee (IDMC) determined that the vaccine was unlikely to demonstrate suitable efficacy.

In its third-quarter earnings report, Sanofi stated, "The safety profile was acceptable, and no signals of vaccine-associated enhanced respiratory disease were observed by the IDMC." Despite this reassurance on safety, the lack of efficacy led to the decision to discontinue the program.

Sanofi's Evolving RSV Portfolio

While the termination of SP0125 represents a setback for Sanofi's pediatric RSV efforts, the company maintains a strong presence in the broader RSV market. Sanofi currently markets Beyfortus, an RSV antibody developed in partnership with AstraZeneca, which has achieved blockbuster status.

The company is also advancing other RSV vaccine candidates, including:

• SP0256: An mRNA vaccine targeting RSV and human metapneumovirus (hMPV) for older adults
• SP0291: An mRNA vaccine targeting RSV, hMPV, and parainfluenza virus type 3 (PIV3) for older adults

In July, Sanofi further expanded its RSV pipeline by acquiring Vicebio for $1.15 billion upfront, gaining access to a non-mRNA RSV vaccine candidate.

Competitive Landscape in RSV Prevention

The RSV vaccine and antibody market has become increasingly competitive, with several major pharmaceutical companies vying for market share:

• GSK's Arexvy and Pfizer's Abrysvo are leading RSV vaccines for older adults
• Moderna's mRESVIA was recently approved, adding to the options for adult vaccination
• Merck & Co.'s Enflonsia, a monoclonal antibody, received FDA approval in June for preventing lower respiratory tract disease from RSV in infants during their first RSV season

As Sanofi refocuses its RSV efforts, the company will likely concentrate on its remaining pipeline candidates and its established presence in the market with Beyfortus. The termination of SP0125 underscores the ongoing challenges in developing effective RSV prevention strategies for young children, a population that remains vulnerable to severe RSV infections.