Invasive pneumococcal infections are serious diseases. Each year in the United States, they account for approximately 50,000 cases of bacteremia (bloodstream infection), 3,000 cases of bacterial meningitis , and 100,000 to 175,000 hospitalizations for pneumonia . Traditionally, these types of infections were treated with penicillin; now certain strains of the bacterium have become resistant to traditional antibiotics, making treatment more difficult. Therefore, researchers are looking for new and effective ways to prevent the infections from occurring in the first place.

Pneumococcal disease is caused by any one of 90 strains of the bacterium Streptococcus pneumoniae. In early 2000, a new vaccine, with proven activity against pneumococcal infections was approved by the FDA for use in infants between the ages of 2 and 23 months, the group considered to be at the highest risk.

Past clinical trials have demonstrated that the vaccine was highly effective against the seven types of Streptococcus pneumoniae believed to be responsible for 80 percent of invasive pneumococcal infections What was not known was how well the vaccine has performed in the population at large since its introduction.

The results of this study, which were published in the May 1, 2003 issue of the New England Journal of Medicine , found that the use of the pneumococcal vaccine not only prevents pneumococcal disease in young children, but may reduce the rate of the disease in adults.

About the study

The researchers examined population-based data from the Active Bacterial Core Surveillance of the Centers for Disease Control and Prevention (a total population of 16 million including 433,591 children under two years of age and 652,551 children between the ages of two and four years).

To assess changes in disease rates after the introduction of the vaccine, the researchers calculated the number of cases of invasive pneumococcal disease in the population using the Active Bacterial Core Surveillance data and U. S. consensus figures. They then compared the percentage of the population with invasive pneumococcal disease in the years following vaccine introduction (2000 and 2001) to the percentage of the population with invasive pneumococcal disease in the years prior to the introduction of the vaccine (1998 and 1999 combined or 1999 alone).

The findings

The researchers found that during the course of the study, the overall rate of invasive pneumococcal infection in the population dropped from an average of 24.3 cases per 100,000 persons prior to vaccine introduction to 17.3 cases per 100,000 after vaccine introduction. The largest decline occurred in children under the age of two years, which showed a 69 percent decrease in the rate of infection after vaccine introduction. In children between the ages of two and three years, the rate of infection dropped by 44 percent.

Disease rates also fell for adults, with the rate of disease after vaccine introduction 32 percent lower in adults between the ages of 20 to 39 years, 8 percent lower in adults between the ages of 40 and 64, and 18 percent lower in adults over 65 years of age. In addition, the rate of infection caused by penicillin-resistant strains of Streptococcus pneumoniae also dropped by 35 percent after vaccine introduction.

How does this affect you?

The researchers concluded that the introduction of the pneumococcal vaccine effectively reduced the rate of invasive pneumococcal infection among young children between the ages of 2 and 23 months, the age group for which it was originally approved.

Additionally, the results of the study suggest that unvaccinated adults are also benefitting from the decreased rate of infection in children. This is most likely a result of decreased transmission of the disease from children to adult parents and caregivers. This is significant because although young children are at the highest risk of invasive disease, most of the more serious cases of pneumococcal disease, as well as most of deaths caused by pneumococcal disease, occur in adults.

Also, multidrug-resistant pneumococci are a worldwide problem and a source of growing concern for public health officials, and numerous programs are being put in place to address this problem. The results of the study indicate that use of the new pneumococcal vaccine is another valuable tool for preventing a substantial number of drug-resistant infections.

Finally, the dream of every public health official and vaccination researcher would be for invasive pneumococcal infections to go the way of small pox and maybe polio – essentially eliminated from the face of the earth. A long way off perhaps, but studies like this one are always encouraging.