In short
Pneumococcal Polysaccharide Serotype 18C is one of ten Streptococcus pneumoniae serotypes contained in Synflorix, a pneumococcal polysaccharide conjugate vaccine authorised in the EU. It is conjugated to tetanus toxoid carrier protein and adsorbed on aluminium phosphate. One completed Phase 2 trial (2023-505154-18-00) evaluated the safety and immunogenicity of a monovalent pneumococcal conjugate candidate containing this serotype in 100 healthy toddlers aged 11 to 15 months.
Key points
- Pneumococcal Polysaccharide Serotype 18C is a component of Synflorix, an authorised pneumococcal conjugate vaccine.
- The serotype is conjugated to tetanus toxoid carrier protein and adsorbed on aluminium phosphate.
- One Phase 2 trial studied a monovalent candidate containing this serotype in 100 healthy toddlers.
- The trial is completed and measured safety and immunogenicity after a 2-dose series.
- Synflorix is given as a 0.5 ml intramuscular injection.
- The marketing authorisation holder is GlaxoSmithKline Biologicals S.A.
What is pneumococcal polysaccharide serotype 18C?
Pneumococcal Polysaccharide Serotype 18C is a purified capsular polysaccharide from the bacterium Streptococcus pneumoniae, chemically linked (conjugated) to a tetanus toxoid carrier protein and adsorbed on aluminium phosphate. In the CTIS product records, it is part of Synflorix, a pneumococcal polysaccharide conjugate vaccine (adsorbed) supplied as a suspension for injection in pre-filled syringes. Synflorix is authorised as a medicine in the European Union, with authorisation records including EU/1/09/508/002 through EU/1/09/508/005, and the authorisation holder is GlaxoSmithKline Biologicals S.A. The NHS dm+d browser classifies the vaccine under ATC code J07AL02, the code for pneumococcal purified polysaccharides conjugated vaccines.
How does pneumococcal polysaccharide serotype 18C work?
Pneumococcal conjugate vaccines work by presenting bacterial polysaccharides attached to a carrier protein to the immune system. The polysaccharide alone is poorly recognised by the immature immune system of infants, but when conjugated to a carrier protein such as tetanus toxoid, it triggers a stronger, T-cell dependent antibody response. The antibodies produced against the serotype 18C polysaccharide help protect against invasive pneumococcal disease caused by that serotype. In the Synflorix product records, serotype 18C is conjugated to tetanus toxoid carrier protein, while other serotypes in the same vaccine are conjugated to protein D derived from non-typeable Haemophilus influenzae or to diphtheria toxoid.
Which conditions is it used or studied for?
- Pneumococcal infections — the Phase 2 trial listed this as the condition studied. Pneumococcal infections include diseases caused by Streptococcus pneumoniae, such as pneumonia, meningitis and bloodstream infections.
- Invasive pneumococcal disease (IPD) — the Medscape review describes how different pneumococcal serotypes cause severe invasive disease, with some serotypes acting as primary pathogens in healthy individuals and others as opportunistic pathogens in at-risk individuals.
How is pneumococcal polysaccharide serotype 18C given?
Synflorix, the vaccine containing serotype 18C, is a suspension for injection given by intramuscular use in a 0.5 ml dose, supplied in pre-filled syringes. The NHS dm+d browser records the formulation as a suspension for injection with a unit dose of 0.5 ml in pre-filled disposable syringes, with packs of 1 or 10 syringes. In the Phase 2 trial, the monovalent candidate containing serotype 18C was administered as a 2-dose series by intramuscular injection to children aged 11 to 15 months.
What do the clinical trials show?
One completed Phase 2 trial (2023-505154-18-00) evaluated a monovalent pneumococcal conjugate candidate in healthy toddlers. The trial enrolled 100 participants aged between 11 and 15 months and tested the candidate as a 2-dose series. The primary outcomes were prompted local reactions (redness, swelling and pain at the injection site), prompted systemic events (fever, decreased appetite, drowsiness or increased sleep, and irritability), adverse events and serious adverse events. The trial also compared the candidate against Synflorix and another investigational product, PF-07831695. The study is completed, meaning data collection has finished.
What side effects are known?
The Phase 2 trial measured safety outcomes including local reactions at the injection site such as redness, swelling and pain, and systemic events such as fever, decreased appetite, drowsiness and irritability. The Medscape review notes that pneumococcal serotypes differ in their potential for colonisation, invasiveness and virulence; serotypes with low invasive potential, such as types 3, 6A, 6B, 8, 19F and 23F, behave as opportunistic pathogens in at-risk individuals, while serotypes with high invasive potential, such as types 1 and 7F, can act as primary pathogens in previously healthy individuals. The supplementary sources provided do not include a full product information list of side effects for Synflorix.