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A Look at Each Vaccine: Pneumococcus Vaccine

What is pneumococcus?

Pneumococcus is a bacterium that causes several different types of serious infections in children. But by far the most common is pneumonia. Children with pneumonia develop high fever, cough, and rapid, difficult breathing. Sometimes the bacteria cause pus to accumulate not only inside the lung, but between the lung and the chest wall (called an empyema). The empyema can compress and collapse the lung. Although the vast majority of children with pneumonia recover, the disease is occasionally fatal.

Much like Haemophilus influenzae type b (Hib), pneumococcal bacteria (Streptococcus pneumoniae) affect the most defenseless of the population (infants and toddlers). The diseases caused by pneumococcus include meningitis, bloodstream infections and pneumonia. Before the pneumococcal vaccine was first introduced for use in all infants in the United States in 2000, every year pneumococcus caused about 700 cases of meningitis, 17,000 cases of bloodstream infections and 71,000 cases of pneumonia. The reason that infants and young children are at greatest risk of serious infection is that they are unable to develop immunity to the sugar (or polysaccharide) that coats the bacteria, something that older children do naturally over time.

An ounce of prevention is worth a pound of cure

In the 1940s all strains of the bacteria pneumococcus were sensitive to the antibiotic, penicillin. However, during the past decade many strains of pneumococcus have become resistant not only to penicillin, but also to the broader-spectrum antibiotics developed more recently to combat bacterial infections. Strains of pneumococcus have now been identified that are highly resistant to most antibiotics. Our reliance on and overuse of antibiotics have backed us into a corner. We have taken our first steps into a post-antibiotic era. This makes the use of vaccines all the more important.

How do you catch pneumococcus?

Pneumococcus is a bacterium that is commonly found lining the surface of the nose and the back of the throat.  About 25 percent of people are colonized with pneumococcus. Many children will come in contact with pneumococcus sometime in the first two years of life. Because most adults have immunity to pneumococcus, a mother will passively transfer antibodies from her own blood to the blood of her baby before the baby is born. The antibodies that the baby gets from her mother usually last for a few months. However, after that time, the baby is unprotected. Most children who first come in contact with pneumococcus don't have a problem. But every year tens of thousands of children suffer severe, often debilitating, and occasionally fatal infections with pneumococcus most of these children were previously healthy and well nourished.

How is the pneumococcal vaccine made?

Like the Hib vaccine, the pneumococcal vaccine is made from the sugar coating (polysaccharide) of the bacteria. Protection against pneumococcus is mediated by antibodies directed against the pneumococcal polysaccharide. By exposing the child to only part of the bacterium, and eliciting a protective immune response, the child will not have to take the risk that his first encounter with natural pneumococcus will result in permanent disabilities or death.

Unfortunately, children less than 2 years old don't develop very good immune responses to this polysaccharide alone. So the pneumococcal vaccine was made in a manner similar to the Hib vaccine. The pneumococcal polysaccharide is linked to a harmless protein. Once linked, young children are now able to make an immune response to the polysaccharide. The big difference between the pneumococcal vaccine and the Hib vaccine is the number of different types of polysaccharides that need to be included in the vaccine. Whereas, there is really only one strain of Hib that causes disease in children, there are about 90 different strains of pneumococcus. Fortunately, most of the serious disease in young children is caused by the seven strains of pneumococcus contained in the vaccine.

The pneumococcal vaccine was found to be highly effective in preventing severe pneumococcal infection (meaning meningitis, bloodstream infections and pneumonia) in a large trial of children injected with the vaccine. About 40,000 children were included in the initial trial of the vaccine. Since 2000 the pneumococcal vaccine has been given to millions of children safely.

Does the pneumococcal vaccine prevent ear infections?

Pneumococcus is a common cause of ear infections in infants and young children. However, other bacteria also cause ear infections in this age group. The pneumococcal vaccine prevents about 7 percent of ear infections and about 20 percent of severe ear infections requiring tubes.

What are the side effects of the pneumococcal vaccine?

Children commonly will have pain or swelling where the shot is given and occasionally low-grade fever. About 1 percent of children will develop a high fever.

Should adults get the pneumococcal vaccine?

The following groups of adults should get the pneumococcal vaccine:

• Adults over the age of 65 because they are at high risk of pneumococcal infections
• Adults with heart or lung disease, liver disease, alcoholism, diabetes or cancer
• Adults without a functioning spleen
• Adults between 19 and 64 years of age who smoke

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Do the benefits of the pneumococcal vaccine outweigh its risks?

Pneumococcal bacteria still cause hundreds of cases of meningitis, bloodstream infections and pneumonia every year in the United States. Because the pneumococcal vaccine does not cause serious side effects, the benefits of the vaccine clearly outweigh its risks.

Reviewed by: Paul A. Offit, MD
Date: November 2008