Pneumococcal polysaccharide serotype 15B de-O-acetylated conjugated to CRM197

Pneumococcal polysaccharide serotype 15B de-O-acetylated conjugated to CRM197 is one of 21 pneumococcal polysaccharides in the 21-valent pneumococcal conjugate vaccine CAPVAXIVE. The full name describes a sugar molecule from the surface of the bacterium Streptococcus pneumoniae, chemically modified (de-O-acetylated) and attached to a carrier protein called CRM197. The product is authorised as a medicine in the EU and supplied by Merck Sharp & Dohme B.V.^[1]

What is pneumococcal polysaccharide serotype 15B de-O-acetylated?

Pneumococcal polysaccharide serotype 15B de-O-acetylated is a bacterial sugar (polysaccharide) from the capsule of Streptococcus pneumoniae serotype 15B. In CAPVAXIVE, this polysaccharide is conjugated to CRM197, a non-toxic mutant of diphtheria toxin, to make it more visible to the immune system. The vaccine contains 21 such polysaccharides, each targeting a different pneumococcal serotype.^[1] The substance is part of a fixed combination product, and the vaccine is authorised in the EU under authorisation record EU/1/25/1913/001.^[1]

How does pneumococcal polysaccharide serotype 15B de-O-acetylated work?

Conjugate vaccines work by linking a bacterial polysaccharide to a carrier protein. The CRM197 carrier protein helps the immune system recognise the polysaccharide and produce antibodies against it. When a person is later exposed to Streptococcus pneumoniae of serotype 15B, these antibodies can help the body fight the infection. This approach is used for all 21 serotypes in CAPVAXIVE.^[1]

Which conditions is it used or studied for?

• Asplenia — people who have had their spleen removed, or whose spleen does not work, are at higher risk of severe pneumococcal infection. One Phase 3 trial is studying the vaccine in 70 asplenic patients.^[1]
• Medium or high risk for pneumococcal invasive infection — a Phase 3 trial is studying vaccination in 1,160 adults at medium or high risk, including during an acute febrile illness.^[2]

How is pneumococcal polysaccharide serotype 15B de-O-acetylated given?

The vaccine is a solution for injection, given as a 0.5 mL intramuscular injection.^[1] The product is a pre-filled syringe. In the trials, the comparator vaccine is Prevenar 20, a 20-valent pneumococcal conjugate vaccine, also given as a 0.5 mL intramuscular injection.^[1][2]

What do the clinical trials show?

Two Phase 3 trials are listed in the registries. The first trial, 2024-515363-63-00, is studying 70 asplenic patients who were vaccinated before or after spleen removal. It measures the mean fold change in pneumococcal serotype-specific IgG antibodies against serotypes common to both PCV20 and PCV21, two to three weeks after a booster vaccination with PCV21, at least 12 months after primary vaccination with PCV20.^[1]

The second trial, NCT06822907, is studying 1,160 adults at medium or high risk for pneumococcal invasive infection. It compares the immune response one month after vaccination during an acute febrile illness with the response one month after vaccination given 15 to 58 days after the illness has resolved. The primary outcome is the proportion of "good responders", defined by seroconversion and a protective IgG level against at least 10 of 13 vaccine serotypes tested.^[2]

Who can take part in these trials?

The asplenia trial includes patients who have had their spleen removed or have a non-functioning spleen, and who were vaccinated with PCV20 before or after splenectomy.^[1] The febrile illness trial includes unvaccinated adults at medium or high risk for pneumococcal infections who have an acute febrile illness at the time of vaccination or who are vaccinated after the illness has resolved.^[2]

What are the trials measuring?

Both trials measure the antibody response to vaccination. The asplenia trial measures the mean fold change in serotype-specific IgG antibodies against common serotypes after a booster dose.^[1] The febrile illness trial measures the proportion of "good responders" — participants who achieve seroconversion (a two-fold or four-fold increase in vaccine-type IgG) and a protective IgG level of at least 1.3 μg/mL for at least 10 of 13 serotypes tested.^[2]

What side effects are known?

The provided sources do not include side effect information for this specific serotype or for CAPVAXIVE. Side effects are not described in the registry data or the supplementary source.