Streptococcus pneumoniae (pneumoncoccus) causes a number of serious illnesses in young children around the world. This bacterium is the leading cause of pneumonia (infection of the lungs), meningitis (infection of the membranes that cover the brain), bacteremia (infection of the bloodstream), sinusitis (infection of the nasal sinuses), and acute otitis media (infection of the middle ear [earaches]) in children less than 5 years of age. In the United States, Streptococcus pneumoniae causes about 17,000 cases/year of invasive disease among children less than 5 years of age. When this bacterium gets into the bloodstream to infect other parts of the body it is called an invasive disease. One example of an invasive disease is meningitis. This bacterium causes 700 cases/year of meningitis and 200 deaths/year in children.
Streptococcus pneumoniae produces a capsule to protect itself from our immune system. Streptococcus pneumoniae makes a capsule that is a carbohydrate polymer (a long chain of sugar molecules). The bacteria place this carbohydrate polymer on the surface of their cells. This capsule inhibits white blood cell phagocytosis (to engulf, surround, eat up; to see a movie of phagocytosis click here). If a white blood cell can phagocytize Streptococcus pneumoniae it is doomed. Our white blood cells are very good at destroying this bacterium once it is inside the white blood cell.
A long time ago it was demonstrated that if we make antibody to a bacterial capsule then white blood cells can phagocytize and destroy the bacteria. Purified capsules from these bacteria are used to immunized people. Most adults and children over 2 years of age will make antibodies to this capsular material and lower their likelihood of getting sick from Streptococcus pneumoniae. Unfortunately, Streptococcus pneumoniae can make up to 90 different types of capsule. If you have antibodies to one capsule type it does not protect you from a Streptococcus pneumoniae producing a different capsule type. To get protection from all the Streptococcus pneumoniae capsule types would require purifying all 90 capsules and then injecting them into people. This is very very costly and filled with problems.
To lower the number of capsular types needed to immunize people investigators determined how many capsule types caused most of the Streptococcus pneumoniae infections. Most studies revealed that in adults about 23 capsule types cause about 89 percent of the infections. Therefore, a Streptococcus pneumoniae (pneumonia, pneumococcal vaccine; PNU-IMMUNE from Wyeth-Ayerst Laboratories and Pneumovax 23 from Merck and Company) vaccine was produced and is given routinely to the elderly and to people with chronic diseases (people with diabetes, asthma, heart problems, no spleen, immunocompromising diseases, etc.).
Unfortunately, children under 2 years of age do not make antibodies when given
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