"We were pretty confident when we recommended this vaccine for children it would help them," says Cynthia Whitney, a researcher on both studies. "What was a pretty pleasant surprise was the amount of benefit we've seen in unvaccinated populations."
Steptococcus pneumoniae, also called pneumococcus, is one of the most common causes of bacterial meningitis in children in the United States. It can also cause bacterial pneumonia and deadly bloodstream infections. In its less severe forms it can also cause ear and throat infections. Pneumococcus bacteria can be found colonizing many people's noses and throats without causing infection. Why it suddenly invades the body and causes disease is unknown.
A vaccine against pneumococcal disease has been available for adults and children over 2 years of age since the 1980s, but in 2000 a new vaccine was approved by the FDA for children 2 to 23 months old.
Whitney and her colleagues have been tracking the incidence of the most severe forms of the disease, invasive pneumococcal disease (IPD) – defined as meningitis or a bloodstream infection, which can include some cases of pneumonia – since the introduction in the vaccine.
"After the first full year we made our first report suggesting the effectiveness of the vaccine. We saw a significant decrease in IPD in target age group," says Whitney. "At that time we weren't sure if it had just been a mild season and the numbers might go back up the next year, or if it was a real downturn due to the vaccine."
The results released today from the second year of surveillance show a continued reduction in IPD rates in children for whom the vaccine is recommended. The rate of IPD in children 2 to 23 months of age from pneumococcal strains that the vaccine protects against was 94% lower in 2002 than it was in 2001. There was also a decline in IPD in older children (age 2-4) and very young children (less than 2 months old) as well.
Another study released today shows a continuing decline in cases of IPD in adults as well. This supports the theory that young children may have been serving as a reservoir for the bacteria in the general population.
"We're vaccinating children and the children in turn are not passing the bacteria on to adults and other children," says Whitney. "Overall, the vaccine has done a great job of preventing disease."
The International Conference on Emerging Infectious Diseases is organized by the Centers for Disease Control and Prevention (CDC), the American Society for Microbiology, the Council of State and Territorial Epidemiologists, the Association of Public Health Laboratories and the World Health Organization. More information on the meeting can be found online at www.iceid.org.