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Pneumococcal polysaccharide serotype 23F conjugated to CRM197 is a vaccine component. The full name describes a sugar molecule (polysaccharide) from the outer coating of one strain — serotype 23F — of the bacterium Streptococcus pneumoniae, chemically linked (conjugated) to a carrier protein called CRM197.[3] CRM197 is a non-toxic, modified form of the diphtheria toxin. The substance belongs to the therapeutic area of bacterial infections and mycoses.[1] It is not used on its own but as one component of pneumococcal conjugate vaccines. In the product records of the EU registry, it appears under the names Pneumococcal Conjugate Vaccine (PCV) and Vaxneuvance suspension for injection in pre-filled syringe.[1] The substance already has a marketing authorisation in the European Union as part of Vaxneuvance, held by Sanofi Pasteur Inc. and Merck Sharp & Dohme B.V.[1] A paediatric formulation exists in two product records.[1]
Polysaccharides from the bacterial capsule alone do not produce a strong immune response in infants. When the serotype 23F polysaccharide is conjugated to the CRM197 carrier protein, the immune system recognises the combination more effectively and produces antibodies against the bacterial sugar.[3] These antibodies help the body defend itself against Streptococcus pneumoniae strains of serotype 23F. The carrier protein in the authorised vaccine Synflorix is protein D from Haemophilus influenzae, tetanus toxoid or diphtheria toxoid depending on the serotype, while the investigational PCV21 uses CRM197 as carrier for all serotypes.[3][2]
The pharmaceutical form is a suspension for injection, given by intramuscular injection.[1] The authorised vaccine Synflorix is supplied in pre-filled syringes or vials, each containing 0.5 ml for one dose; one dose contains 1 microgram of pneumococcal polysaccharide serotype 23F adsorbed on aluminium phosphate.[3] The trials use the same route of administration, intramuscular injection.[1] The MHRA paediatric investigation plan for the CRM197-conjugated vaccine also describes a suspension for injection for intramuscular use.[2]
The EU registry lists one Phase 3 interventional trial for this substance, with status Authorised.[1] The trial is studying a 21-valent pneumococcal conjugate vaccine (PCV21) in 1,113 healthy infants from approximately 2 months of age.[1] The substance appears in this trial both as the test product (as part of PCV21) and as a comparator (as part of the authorised 15-valent vaccine Vaxneuvance).[1]
The primary outcomes measure the antibody response. The trial aims to demonstrate that the immune response induced by PCV21 is not inferior to the 15-valent vaccine for the shared serotypes, and superior for the six serotypes unique to PCV21.[1] The response is assessed by the seroresponse rate — the proportion of infants who produce a defined level of antibodies — and by the geometric mean concentration (GMC) of immunoglobulin type G (IgG) antibodies, measured 30 days after the toddler dose.[1]
The participants are healthy full-term and preterm infants. The study measures outcomes after the toddler dose, which is the third dose for full-term infants and the fourth dose for preterm infants.[1]
The supplementary sources provided do not contain specific side effect information for pneumococcal polysaccharide serotype 23F conjugated to CRM197. The Norfolk and Waveney Formulary lists pneumococcal conjugate vaccines as non-formulary items but does not describe side effects.[4] The BMJ Open study of the 23-valent polysaccharide vaccine in older patients with chronic pulmonary disease does not report adverse events for the CRM197-conjugated product.[5] No side effect data can therefore be stated from the provided sources.
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