RAHWAY, N.J. – September 11, 2025 – Merck (NYSE: MRK), known as MSD outside the United States and Canada, today announced that its investigational pneumococcal 21-valent conjugate vaccine CAPVAXIVE® demonstrated robust immune responses and favorable safety outcomes in children and adolescents at increased risk of pneumococcal disease. The results, from the pivotal Phase 3 STRIDE-13 trial, were presented at the 6th European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Conference on Vaccines in Lisbon, Portugal.

Science Significance

Pneumococcal disease remains a global health burden, particularly for vulnerable populations with chronic medical conditions. CAPVAXIVE®, which includes nine serotypes not covered by the long-standing PPSV23 vaccine, was shown to elicit immune responses across all 21 serotypes studied.

In STRIDE-13, CAPVAXIVE was noninferior to PPSV23 for the 12 shared serotypes and superior for each of the nine unique serotypes. These findings demonstrate the scientific advancement of next-generation conjugate vaccines designed to provide broader protection against invasive pneumococcal disease (IPD).

Regulatory Significance

Merck announced it will share the full STRIDE-13 data with global regulatory authorities. The company already holds approvals for CAPVAXIVE in the U.S., EU, Japan, and multiple other countries, under accelerated approval pathways tied to immunogenicity endpoints.

Continued approval is contingent upon confirmatory evidence of clinical benefit, making STRIDE-13’s final readout a critical milestone in supporting ongoing regulatory discussions worldwide. The favorable safety and immunogenicity profile strengthens the vaccine’s standing in post-approval evaluations.

Business Significance

For Merck, CAPVAXIVE represents a strategic anchor in its vaccines portfolio. Designed initially for adults, the expansion of evidence into pediatric and adolescent high-risk populations enhances the vaccine’s market potential. According to CDC data, CAPVAXIVE’s serotype coverage spans approximately 84% of IPD cases in adults and 78% in children and adolescents with chronic conditions.

The ability to position CAPVAXIVE as a broad-spectrum pneumococcal solution across age groups is expected to significantly boost its commercial trajectory, ensuring competitiveness against existing pneumococcal vaccines such as PCV20.

Patients’ Significance

Children and adolescents with chronic diseases such as diabetes, chronic lung disease, or heart conditions face elevated risks of severe pneumococcal illness. By demonstrating superior protection against nine additional serotypes, CAPVAXIVE offers these vulnerable populations a critical opportunity for broader coverage without added safety concerns.

The trial confirmed comparable adverse event rates between CAPVAXIVE and PPSV23, with injection-site reactions slightly higher but manageable. For families and clinicians, this represents an encouraging step toward safer, more effective vaccination options for high-risk children.

Policy Significance

Pneumococcal vaccination strategies are central to global immunization agendas. The expansion of coverage to additional serotypes aligns with public health objectives to reduce hospitalizations, antibiotic use, and healthcare costs tied to pneumonia, meningitis, and bacteremia.

The STRIDE-13 results may influence immunization policy bodies such as the U.S. ACIP, the European Medicines Agency, and national immunization technical advisory groups to consider CAPVAXIVE for pediatric recommendations, especially for children at increased risk of IPD. This could reshape guidelines and further support sustainable healthcare planning.

Transaction Highlights

The Phase 3 STRIDE-13 trial enrolled 882 children and adolescents aged 2 to <18 years, randomized to receive either CAPVAXIVE or PPSV23 following completion of their primary pneumococcal vaccine series. At 30 days post-vaccination, CAPVAXIVE demonstrated immunogenicity for all 21 serotypes, with superior immune responses for nine unique serotypes compared to PPSV23. Safety outcomes were consistent with expectations, with no significant differences in systemic or serious adverse events.

These data represent the final readout of the STRIDE clinical program. Merck will now advance discussions with regulatory authorities globally, aiming to expand CAPVAXIVE’s indication into pediatric populations at elevated risk.

Source: Merck & Co., Inc. Press Release