Pneumococcal Vaccine Elicits Immune Responses to 21 Serotypes in Children With 1 or More Health Conditions

This week, at the ongoing European Society of Clinical Microbiology and Infectious Diseases (ESCMID) Conference, Merck announced positive results from its phase 3, STRIDE-13 trial, for its vaccine, Capvaxive, a pneumococcal 21-valent conjugate vaccine, which examined a vulnerable pediatric population. The findings show the vaccine has the potential to provide additional protection in individuals 2-17 years old by covering approximately 78% of invasive pneumococcal disease (IPD) cases, with 11 unique serotypes that account for approximately 34% of IPD cases, based on national-level Centers for Disease Control and Prevention (CDC) data from 2019-2023.¹

According to the company, the vaccine was found to be superior to the PPSV23 vaccine for each of the nine serotypes unique to Capvaxive, as measured by serotype-specific OPA GMTs at 30 days post-vaccination, which was the primary immunogenicity endpoint.¹

Study Specifics

The study examined the safety, tolerability, and immunogenicity of Capvaxive compared to PPSV23 in children and adolescents aged 2 to 17 years of age who have completed a primary pediatric pneumococcal vaccination regimen and have 1 or more chronic medical conditions that put them at an increased risk of pneumococcal disease. Conditions included diabetes, chronic compensated liver disease, chronic lung disease, chronic heart disease, or chronic kidney disease.¹

The study enrolled 882 participants who were randomized 3:2 to receive a single dose of Capvaxive or PPSV23.

Although the vaccine was designed for adults and is currently approved for individuals 18 years of age and older, the pediatric population can benefit from this vaccine.

“While Capvaxive was designed to specifically cover the serotypes that cause the majority of invasive pneumococcal disease (IPD) cases in adults, findings from STRIDE-13 underscore its added potential to help protect children and adolescents who are at an increased risk,” Paula Annunziato, MD, senior vice president, infectious diseases and vaccines, Global Clinical Development, Merck Research Laboratories, said in a statement.¹

Learn more: Capvaxive’s EU Approval and Impact on Pneumococcal Disease Prevention: A Focus on At-Risk Populations

A STRIDE-13 trial investigator concurred with this opinion. “Children and adolescents living with chronic medical conditions are at increased risk of pneumococcal disease and offering them additional protection is essential,” Rotem Lapidot, MD, chief of Pediatric Infectious Diseases at Rambam Health Care Campus, said in a statement. “Results from STRIDE-13 demonstrate the potential of Capvaxive to deliver protection for these vulnerable populations, who may benefit from additional pneumococcal disease coverage by including serotypes not contained in other approved pneumococcal infant regimens.”¹

Merck reported the proportions of participants with adverse events (AEs), including systemic and serious vaccine-related AEs, were generally comparable between groups, which was identified as the primary safety endpoint.¹

The Vaccine’s Current Indications

The vaccine has been approved in several countries including the United States, Canada, Australia, European Union, Japan, and others. In adults, Capvaxive provides protection against the serotypes responsible for approximately 84% of IPD cases in adults 50 years of age and older, compared to approximately 52% covered by PCV20 (pneumococcal 20-valent conjugate vaccine), based on national-level CDC data from 2018-2022.¹

The CDC’s Advisory Committee on Immunization Practices recommended the use of the vaccine for all adults aged ≥65 years, as well as adults aged 19–64 years with certain risk conditions for pneumococcal disease if they have not received the vaccine, or whose vaccination history is unknown.²

It is currently indicated in the US for the following:

• Active immunization for the prevention of invasive disease and pneumonia caused by Streptococcus pneumoniae serotypes 3, 6A, 7F, 8, 9N, 10A, 11A, 12F, 15A, 15B, 15C, 16F, 17F, 19A, 20A, 22F, 23A, 23B, 24F, 31, 33F and 35B in individuals 18 years of age and older;
• Active immunization for the prevention of pneumonia caused by S. pneumoniae serotypes 3, 6A, 7F, 8, 9N, 10A, 11A, 12F, 15A, 15C, 16F, 17F, 19A, 20A, 22F, 23A, 23B, 24F, 31, 33F and 35B in individuals 18 years of age and older.

Regarding this latest data, Merck said this represents the final readout of the phase 3 STRIDE clinical program and will be shared with global regulatory authorities.

References
1.CAPVAXIVE (Pneumococcal 21-valent Conjugate Vaccine) Demonstrates Positive Immune Responses in Children and Adolescents at Increased Risk of Pneumococcal Disease. Merck press release. September 11, 2025. Accessed September 12, 2025.
2.Kobayashi M, Leidner AJ, Gierke R, et al. Use of 21-Valent Pneumococcal Conjugate Vaccine Among U.S. Adults: Recommendations of the Advisory Committee on Immunization Practices — United States, 2024. MMWR Morb Mortal Wkly Rep 2024;73:793–798. DOI: http://dx.doi.org/10.15585/mmwr.mm7336a3