Pneumococcal polysaccharide serotype 24F conjugated to CRM197

Table of contents

• What is pneumococcal polysaccharide serotype 24F?
• How does pneumococcal polysaccharide serotype 24F work?
• Which conditions is it used or studied for?
• How is pneumococcal polysaccharide serotype 24F given?
• What do the clinical trials show?
• What side effects are known?

What is pneumococcal polysaccharide serotype 24F?

Pneumococcal polysaccharide serotype 24F conjugated to CRM197 is a polysaccharide from the bacterium Streptococcus pneumoniae (pneumococcus) chemically linked to a carrier protein called CRM197, a non-toxic variant of diphtheria toxin.^[3] The full substance name in the registry is Pneumococcal polysaccharide serotype 24F conjugated to CRM197. It is one of 21 serotype components in the vaccine CAPVAXIVE, a pneumococcal polysaccharide conjugate vaccine (21-valent).^[1] The product is authorised as a medicine in the European Union under authorisation record EU/1/25/1913/001, held by Merck Sharp & Dohme B.V.^[1] The same serotype 24F component also appears in the investigational 15-valent vaccine V114.^[3]

How does pneumococcal polysaccharide serotype 24F work?

Pneumococcal polysaccharide serotype 24F is a conjugate vaccine component. The polysaccharide from the pneumococcal serotype 24F capsule is attached to the CRM197 carrier protein, which helps the immune system recognise the polysaccharide and produce antibodies against it.^[3] These antibodies are directed against the polysaccharide capsule of serotype 24F pneumococci, so the vaccine prepares the immune system to defend against infections caused by this serotype.^[3]

Which conditions is it used or studied for?

The vaccine containing serotype 24F is used to help protect against pneumococcal disease, including invasive infections caused by Streptococcus pneumoniae. The clinical trials in the registry are studying it in two specific groups:

• Asplenia — people without a spleen, who are at increased risk of severe pneumococcal infection. One Phase 3 trial is testing the vaccine in asplenic patients vaccinated before or after spleen removal.^[1]
• Medium or high risk for pneumococcal invasive infection — a second Phase 3 trial is testing the vaccine in adults with an acute febrile illness who are at medium or high risk for pneumococcal infections.^[2]

How is pneumococcal polysaccharide serotype 24F given?

The vaccine containing serotype 24F is a solution for injection in a pre-filled syringe. It is given as an intramuscular injection of 0.5 ml.^[1] In the registered trials, the product is CAPVAXIVE solution for injection in pre-filled syringe, described as Pneumococcal polysaccharide conjugate vaccine (21-valent).^[1]

What do the clinical trials show?

Two Phase 3 trials are registered for the vaccine containing serotype 24F. Both are interventional studies and both are currently authorised but not yet recruiting.^[1][2]

Who can take part in these trials?

The first trial (2024-515363-63-00) includes 70 participants with asplenia, vaccinated either before or after spleen removal.^[1] The second trial (NCT06822907) includes 1,160 adults with an acute febrile illness who are at medium or high risk for pneumococcal invasive infection.^[2]

What are the trials measuring?

The asplenia trial measures the mean fold change in pneumococcal serotype-specific IgG antibody concentrations (GMCs) against serotypes common to PCV20 and PCV21, 2–3 weeks after a booster vaccination with PCV21, at least 12 months after primary vaccination with PCV20.^[1] The febrile illness trial measures the proportion of immune "good responders" to PCV-20 or PCV-21 at 1 month after vaccination. A good responder is defined by a 2-fold increase in vaccine-type IgG after vaccination for at least 10 of 13 tested serotypes, together with an immune protective response defined as ELISA IgG of at least 1.3 μg/mL in at least 10 of 13 tested serotypes.^[2] Both trials compare CAPVAXIVE (PCV21) with Prevenar 20 (PCV20), a 20-valent pneumococcal conjugate vaccine.^[1][2]

What side effects are known?

The supplementary source provided does not contain information on side effects for serotype 24F or the vaccines containing it.^[3] Side effect information is therefore not included on this page.