Pneumococcal disease is a significant concern to children’s health worldwide, estimated to result in more than one million deaths each year in young children in developing countries, mostly due to pneumonia.
In industrialised nations, the annual incidence of invasive pneumococcal disease (IPD) in children younger than two years of age may be as high as 160 cases per 100 000. Furthermore, antibiotic-resistant strains have made treatment of pneumococcal infections increasingly difficult. As a result, the need for an effective vaccine is especially important.
What is pneumococcal disease?
Pneumococcal disease describes a group of illnesses caused by the bacterium Streptococcus pneumoniae, also known as pneumococcus. This bacterial pathogen, which affects both children and adults, is a major cause of disease and death worldwide. Because there are more than 90 different serotypes of S. pneumoniae, development of effective vaccines has proven to be more challenging than with other diseases such as Haemophilus influenzae type b (Hib).
After pneumococcus colonises the upper respiratory tract, it can cause several types of disease. One type of disease is invasive pneumococcal disease (IPD), where S. pneumoniae is isolated from the blood or another normally sterile site. Invasive pneumococcal diseases include bacteraemia (bacterial infection of the blood), sepsis (an infection in the blood), meningitis (bacterial infection of the lining of the spinal cord and brain), and bacteraemic pneumonia (an infection of the lung). The spread of pneumococcus from the nasopharynx to the upper and lower respiratory tract can result in noninvasive pneumococcal diseases, including bacterial pneumonia, acute otitis media (inflammation of the middle ear) and sinusitis (infection of the sinuses). In cases of untreated patients or treatment failure, pneumococcal disease can lead to hearing loss, paralysis and sometimes death.
The recognition of the impact of S. pneumoniae disease varies by country. In Latin American, African and Asian Pacific countries, one of the most common concerns is pneumococcal pneumonia. In fact, in several Latin American countries, pneumonia accounted for about 40% to 60% of all cases of pneumococcal disease. S. pneumoniae also has been associated with the highest morbidity and mortality of bacterial meningitis in children. Annual rates of meningitis in European children range from 0.5 to 12.6 cases per 100 000 children.
Increased childhood risk
Certain factors increase a child’s risk of contracting a pneumococcal infection:
- Age: Children younger than two years old are at increased risk.
- Underlying medical conditions: Medical conditions such as sickle cell disease, HIV, diabetes, pulmonary disease and asplenia predispose children to pneumococcal disease.
- Out-of-home child care: Children who attend out-of-home child care are at increased risk of contracting pneumococcal disease.
In countries in which pneumococcal disease has been studied, findings show that younger children have a greater chance of contracting an IPD than older children.
Pneumococcus is commonly found in the nose and throat of healthy children and adults. Individuals who carry pneumococcus in their nasopharynx can potentially infect others through close contact or airborne particles, such as those found in sneezes or coughs, though not all individuals who have exposure to infection will become ill.
The colonisation of pneumococci in young children is very common. Children are, therefore, both major carriers and victims of pneumococcal disease.
The signs and symptoms of pneumococcal disease vary by illness:
- Bacteraemia may include high fever associated with other nonspecific signs of illness.
- Meningitis may include fever, severe headache, vomiting, drowsiness, aggression and stiff neck in older children; in infants, more frequent symptoms are fever, vomiting, irritability, high-pitched cries and other nonspecific signs of illness.
- Pneumonia may include sudden shaking, chills, cough, fever and chest congestion.
- Acute otitis media (middle ear infection) may include earache, fever and temporary hearing loss. In infants and young children, nausea, vomiting, diarrhoea and fever may signal acute otitis media.
- Acute sinusitis may include low-grade fever, runny nose and cough.
IPD is diagnosed when the organism is cultured from blood or from other normally sterile sites. In contrast, physical examinations and x-rays are used to diagnose noninvasive diseases, including acute otitis media and nonbacteraemic pneumococcal pneumonia.
Antibiotic resistance: A growing concern
In the past, pneumococcal disease could be treated effectively with beta-lactam antibiotics, which included penicillin and cephalosporin. In the last 30 years, however, there has been an increase in S. pneumoniae strains that are resistant to penicillin and other antibiotics, and the prevalence of these strains continues to increase worldwide. Based on limited laboratory reports, more than 60% of penicillin non-susceptible strains in South Africa are caused by 7 serotypes, and these serotypes also account for more than 57% of IPD in children aged 6 months to 23 months. Children infected with drug-resistant strains may experience prolonged illness and therefore require treatment with expensive alternative antibiotics and hospitalisation.
Prevention through vaccination
With the rise in antibiotic-resistant pneumococci and persistent morbidity and mortality in spite of modern medicine, the focus of disease management has shifted from treatment to prevention. Until recently, polysaccharide vaccines were the only form of protection against pneumococcal disease; however, they do not stimulate an adequate immune response in infants and young children.
Wyeth S.A. (Pty) Limited have recently introduced to South Africa a conjugate vaccine which is the first pneumococcal conjugate vaccine to help provide protection for infants and young children against pneumococcal disease caused by the seven most common paediatric serogroups of S. pneumoniae. As a conjugate vaccine, it helps provide protection that was previously unavailable to infants and young children by stimulating the immune system and helping to create immunologic memory (i.e. the body will "remember" the specific group of microrganisms, and mount a better immune response next time it is confronted by them, thus preventing illness).
In prelicensure clinical trials, the most frequently reported adverse events of the pneumococcal conjugate vaccine included injection site reactions, fever >38 degrees Celsius, irritability, drowsiness, restless sleep, decreased appetite, vomiting, diarrhoea, and rash or hives.