Sanofi Halts RSV Vaccine Program 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. This development 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, codenamed 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, faced an early end when the 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 halt the program entirely.

Shifting Focus in RSV Pipeline

While the failure 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 not abandoning its RSV research efforts, however. Sanofi's pipeline includes mRNA vaccines for older adults, such as SP0256 targeting RSV and human metapneumovirus (hMPV), and SP0291, which targets RSV, hMPV, and parainfluenza virus type 3 (PIV3). These candidates are currently in clinical trials.

Competitive Landscape in RSV Prevention

The RSV vaccine and treatment market has become increasingly competitive. GSK's Arexvy and Pfizer's Abrysvo lead the market for older adults, with Moderna's recently approved mRESVIA joining the fray. In the pediatric space, Sanofi and AstraZeneca's Beyfortus now faces competition from Merck & Co.'s Enflonsia, which received FDA approval in June for preventing lower respiratory tract disease from RSV in infants during their first RSV season.

Sanofi's recent $1.15 billion upfront acquisition of Vicebio for its non-mRNA RSV vaccine further underscores the company's commitment to maintaining a strong position in the RSV market, despite the setback with SP0125.