Sanofi Targets Pfizer’s Pneumococcal Stronghold With New Phase 3 Infant Vaccine Trial

Sanofi SA (SNY) announced an update on their ongoing clinical study.

Study Overview

Sanofi has launched a Phase 3 trial titled “A Phase 3, Randomized, Modified Double-blind, Active-controlled, Parallel-group, Lot-to-lot Consistency, 4-arm Study to Investigate the Safety and Immunogenicity of a 4-dose Regimen of a 21-valent Pneumococcal Conjugate Vaccine in Healthy Infants and Toddlers.” The study will test whether three separate manufacturing lots of Sanofi’s new 21-valent pneumococcal conjugate vaccine (PCV21) work the same way and are as safe as Pfizer’s approved 20-valent vaccine (Prevnar 20) in infants starting at about two months of age. For investors, this is a late-stage move in a large, established vaccine market where new entrants with broader coverage and reliable manufacturing can shift long-term revenue streams.

Intervention/Treatment

The main treatment is Sanofi’s investigational 21-valent pneumococcal conjugate vaccine (PCV21), given as an injection to help infants build protection against more strains of pneumococcal bacteria than current standard options. Three different PCV21 manufacturing lots will be tested. The control arm uses an approved 20-valent pneumococcal conjugate vaccine (20vPCV, Prevnar 20), representing today’s standard of care. Routine childhood vaccines such as Vaxelis, rotavirus, MMR, varicella, and hepatitis A are given alongside the study vaccines to mirror real-world pediatric practice.

Study Design

This is an interventional Phase 3 trial with randomized assignment to four groups: three PCV21 groups (each receiving a different lot) and one control group receiving the licensed 20-valent vaccine. The model is parallel, meaning each infant stays in the same group for all four doses at 2, 4, 6, and 12 months of age. The design is “modified double-blind” with quadruple masking: parents, care teams, investigators, and outcome assessors do not know which vaccine a child receives, while only a small group of staff preparing injections is unblinded for practical reasons. The main goal is prevention—showing PCV21 provides similar immune response and safety to the approved 20-valent vaccine, and that all three PCV21 lots behave consistently.

Study Timeline

The study was first submitted on January 15, 2026, signaling the formal start of regulatory and site-setup activities. At this stage, the trial is listed as “Not Yet Recruiting,” so enrollment of infants has not begun. The same date, January 15, 2026, is recorded as the most recent update, showing this is a fresh entry on the registry. Primary completion and final completion dates are not yet specified, but given a follow-up of about 17 months per participant and typical enrollment ramp-up, investors should expect first top-line immunogenicity data no earlier than 2–3 years after recruitment begins, with final safety and consistency data following thereafter.

Market Implications

This new Phase 3 trial underscores Sanofi’s push to expand its pediatric vaccine franchise into higher-valent pneumococcal products, directly challenging Pfizer’s Prevnar 20 in a highly profitable, global market. A successful PCV21—with more bacterial strain coverage and proof of lot-to-lot consistency—could support a differentiated label, strengthen Sanofi’s competitive position in pediatric vaccines, and help diversify revenue beyond flu and adult vaccines. In the near term, the update is unlikely to move Sanofi’s share price dramatically given the very early stage of this specific study and the long path to approval. However, it reinforces the long-term pipeline story, which tends to support sentiment among long-horizon investors and healthcare-focused funds. For Pfizer, the trial highlights growing competition risk around its pneumococcal franchise, though actual market share pressure would not materialize until after a potential PCV21 approval. Overall, this update is incremental but positive for Sanofi’s strategic positioning in vaccines and will be tracked alongside other late-stage assets in its portfolio.

The study is currently ongoing in setup with the latest information available on the ClinicalTrials portal.

To learn more about SNY’s potential, visit the Sanofi SA drug pipeline page.