Pneumococcal polysaccharide serotype 15A conjugated to CRM197

Pneumococcal polysaccharide serotype 15A conjugated to CRM197 is a component of the pneumococcal polysaccharide conjugate vaccine (21-valent) sold under the name CAPVAXIVE. The substance is a chemically conjugated polysaccharide that forms part of a vaccine designed to protect against infections caused by the bacterium Streptococcus pneumoniae. CAPVAXIVE is authorised as a medicine in the European Union, with the authorisation held by Merck Sharp & Dohme B.V.^[1]

The table of contents below shows what this page covers.

Table of contents

• What is pneumococcal polysaccharide serotype 15A?
• How does pneumococcal polysaccharide serotype 15A work?
• Which conditions is it used or studied for?
• How is pneumococcal polysaccharide serotype 15A given?
• What do the clinical trials show?
• Who can take part in these trials?
• What are the trials measuring?
• Ongoing research and future directions

What is pneumococcal polysaccharide serotype 15A?

Pneumococcal polysaccharide serotype 15A conjugated to CRM197 is a vaccine component made from the sugar coating (polysaccharide) of one specific strain of Streptococcus pneumoniae, chemically linked to a carrier protein called CRM197. It is one of 21 serotype components in CAPVAXIVE, a pneumococcal polysaccharide conjugate vaccine (21-valent) authorised as a medicine in the European Union.^[1]

The full registry name lists 21 serotypes conjugated to CRM197, including serotype 15A, serotype 3, serotype 6A, serotype 7F, serotype 19A, and others.^[1] The product name under which this combination is supplied is CAPVAXIVE solution for injection in pre-filled syringe.^[1]

How does pneumococcal polysaccharide serotype 15A work?

Pneumococcal conjugate vaccines work by presenting bacterial polysaccharides linked to a carrier protein to the immune system. The CRM197 carrier protein helps the immune system recognise the polysaccharide and produce antibodies against it. These antibodies can then help protect against infections caused by Streptococcus pneumoniae strains carrying that serotype. The clinical trials for this substance measure the antibody response in people who receive the vaccine.^[1][2]

Which conditions is it used or studied for?

• Asplenia — a condition in which a person has no spleen, either from birth or after surgical removal. People without a spleen are at higher risk for serious pneumococcal infections, and one trial studies how well vaccination works in these patients.^[1]
• Medium or high risk for pneumococcal invasive infection — adults who have underlying conditions that make them more vulnerable to severe pneumococcal disease. A second trial studies vaccination in these patients, including during an acute febrile illness.^[2]

How is pneumococcal polysaccharide serotype 15A given?

The vaccine is supplied as a solution for injection in a pre-filled syringe and is given by intramuscular injection. In the clinical trials, each dose is 0.5 millilitres.^[1][2]

What do the clinical trials show?

Two Phase 3 interventional trials are registered for this vaccine component as part of CAPVAXIVE. Both are authorised, meaning they have received regulatory approval to proceed. The trials compare CAPVAXIVE (21-valent) with Prevenar 20, a 20-valent pneumococcal conjugate vaccine.^[1][2]

The smaller trial enrols 70 participants with asplenia and examines the response to a booster vaccination with CAPVAXIVE at least 12 months after primary vaccination with Prevenar 20, in patients primed before or after splenectomy.^[1] The larger trial enrols 1,160 participants at medium or high risk for pneumococcal invasive infection and compares the immune response when vaccination is given during an acute febrile illness versus 15–58 days after the illness has resolved.^[2]

Who can take part in these trials?

The asplenia trial is open to patients without a spleen, vaccinated either before or after spleen removal.^[1] The second trial is open to unvaccinated patients at medium or high risk for pneumococcal infections who are experiencing an acute febrile illness at the time of enrolment.^[2]

What are the trials measuring?

Both trials measure the immune response as their primary outcome. The asplenia trial measures the mean fold change in serotype-specific immunoglobulin G (IgG) concentrations against serotypes common to both vaccines, 2–3 weeks after booster vaccination.^[1] The febrile illness trial measures the proportion of \"good responders\" at 1 month after vaccination, defined by seroconversion — a 2-fold or 4-fold increase in vaccine-type IgG — for at least 10 of 13 tested serotypes, together with a protective IgG level of at least 1.3 μg/mL.^[2]

Ongoing research and future directions

Both trials are currently in the authorised stage, meaning they are approved to proceed but results are not yet reported in the registries. The research focuses on whether the vaccine produces adequate immune responses in people with asplenia and whether vaccination during an acute febrile illness is as effective as waiting until recovery.^[1][2]