Rates of pneumococcal meningitis, a potentially life-threatening infection, have declined substantially since a new vaccine was introduced in 2000, a new study shows.

The declines have been seen not only in children given the vaccine but also in adults, suggesting a herd immunity effect, the researchers noted. To assess the effect of the vaccine, researchers from several universities analyzed surveillance data from 1998 to 2005 in eight states.

Overall, the number of cases of the disease dropped 30 percent in that time, but the effect on the very youngest and oldest was even more pronounced: Incidence decreased by 64 percent in those younger than 2 and by 54 percent in those older than 65.

"This vaccine has really had a very profound effect on the incidence of pneumococcal disease," said study co-author Dr. Nancy Bennett, a professor of medicine at the University of Rochester Medical Center, in New York. The report appears in the Jan. 15 issue of the New England Journal of .

The study goes beyond previous research in terms of looking at population groups as well as different forms of Streptococcus pneumoniae, which causes pneumococcal meningitis, an inflammation of the meninges, or membranes, surrounding the brain and spinal cord.

"This is a pretty comprehensive study looking at a number of different serotypes [groupings of bacteria within a family] and all age groups. It gets a nice survey of the population," said Jeffrey Cirillo, an associate professor of microbial and molecular pathogenesis at Texas A&M Health Science Center College of Medicine, in College Station. "It is only in eight states so it's not throughout the entire country, but it's probably the most comprehensive analysis, and no one else had looked at it over that long of a period."

The vaccine, known as Prevnar and made by Wyeth Pharmaceuticals, is part of the standard vaccination recommendation for children in the United States ages 2 to 23 months, as well as for children 24 to 59 months old who are at high risk for pneumococcal disease.

Since the vaccine came out in 2000, there have been a number of studies reporting on its effect on meningitis and blood infections.

"This is the first to focus specifically on meningitis," Bennett said.There was a 73.3 percent decrease in the incidence of PCV7 serotype (bacteria types covered by the vaccine) in all age groups. Researchers also found declines in antibiotic-resistant serotypes not specifically targeted by the vaccine.

"There were small increases in the rates of meningitis caused by serotypes that are not included in the vaccine," Bennett noted. The study reported a 60.5 percent increase in cases of meningitis types not protected by the vaccine, but Bennett said that "even a 60 percent increase in something that doesn't happen much has a small effect overall."

The increases were "outweighed by the overall decrease in disease," she said.

However, she continued, "it is something that we need to closely observe and that will be addressed with vaccines that cover more serotypes."

Prevnar was developed by researchers at the University of Rochester, who sold the technology to Wyeth, according to a university spokesman. Several authors of the study, including Bennett, have received funding from Wyeth and other pharmaceutical companies.

Cirillo described the study results as "very promising."

"This is a pretty significant finding, especially the large impacts the vaccine has on serotypes it covers," he said. "And within the serotypes that were covered, the efficacy was up to about 90 percent," referring to certain groups that showed the incidence of pneumococcal meningitis decreasing by almost 93 percent. That's amazing."

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