Synflorix is a vaccine developed by GlaxoSmithKline (GSK) to protect infants and young children globally from diseases caused by the bacterium Streptococcus pneumoniae. Its design as a conjugate vaccine allows it to stimulate a strong immune response, establishing protection early in life. Synflorix is an inactivated vaccine, meaning it contains components of the bacteria rather than the live organism, and is administered as a suspension by intramuscular injection.
Pneumococcal Disease and Targeted Strains
Pneumococcal disease is a range of illnesses caused by Streptococcus pneumoniae, commonly known as pneumococcus. This bacterium can cause non-invasive illnesses like acute otitis media and serious, life-threatening conditions. The severe forms, called Invasive Pneumococcal Disease (IPD), occur when the bacteria invade sterile sites, leading to infections like meningitis, sepsis, and bacteremic pneumonia. Synflorix is a 10-valent pneumococcal conjugate vaccine (PCV10), targeting ten specific serotypes responsible for a large proportion of pneumococcal diseases in children worldwide. The vaccine includes the capsular polysaccharides from the following serotypes:
- 1
- 4
- 5
- 6B
- 7F
- 9V
- 14
- 18C
- 19F
- 23F
How Conjugate Vaccines Provide Protection
The immune system of young infants often struggles to recognize the polysaccharide capsule surrounding Streptococcus pneumoniae, the component traditional vaccines use. Polysaccharides alone are T-cell independent antigens, failing to stimulate a lasting memory response in children under two years of age. Conjugate vaccines, like Synflorix, overcome this limitation by chemically linking the polysaccharide to a protein carrier. In Synflorix, the bacterial polysaccharides are conjugated to one of three carrier proteins: protein D from non-typeable Haemophilus influenzae (NTHi), tetanus toxoid, or diphtheria toxoid. When the immune system encounters the vaccine, specialized cells process the linked components, activating helper T cells and generating immunological memory.
Dosing Guidance and Target Populations
Synflorix is primarily indicated for active immunization in infants and children from six weeks up to five years of age. Standard immunization series vary by national guidelines but typically involve a two- or three-dose primary schedule followed by a booster. A common primary series for infants starting at six weeks consists of three doses given at least one month apart. This is followed by a booster dose in the second year of life (12 to 15 months) for optimal long-term protection. The vaccine is administered by intramuscular injection, usually into the thigh in infants or the deltoid muscle in older children.
Known Side Effects and Safety Profile
The vaccine is generally well-tolerated, with most adverse reactions being mild to moderate in severity and temporary. The most frequently reported adverse reactions after primary vaccination are local reactions at the injection site, such as redness, pain, and swelling. Systemic side effects are also common, occurring in more than one in ten vaccinated individuals, and include irritability, fever, drowsiness, and loss of appetite. As with any injectable vaccine, there is a very rare risk of a severe allergic reaction, such as anaphylaxis.
Synflorix in Global Immunization Programs
Synflorix plays an important role in public health efforts aimed at reducing childhood mortality worldwide. It is a significant component of programs supported by organizations like Gavi, the Vaccine Alliance, which improves access to vaccines for children in low and middle-income countries. Through innovative financing, Synflorix is supplied to Gavi-eligible countries at a substantially discounted price. The choice to use Synflorix (PCV10) over other pneumococcal conjugate vaccines often involves considerations of cost-effectiveness and regional serotype prevalence. To facilitate deployment in areas with challenging infrastructure, the World Health Organization has prequalified a four-dose vial presentation, which reduces the cold-chain volume needed for storage and transport.