A routine childhood vaccine used to prevent several common types of infections has helped cut the rate of a deadly form of meningitis by 30 percent in children and adults, U.S. researchers said on Wednesday, suggesting even the unvaccinated are benefiting from the shot.

They said the vaccine Prevnar made by Wyeth significantly reduced cases of meningitis caused by pneumococcal bacteria strains covered by the vaccine.

But they also noted a worrisome increase of pneumococcal meningitis in strains not covered by the vaccine and those that resist antibiotics.

“When you immunize children, they are much less likely to carry pneumococcal strains covered by the vaccine in the back of the throat,” Dr. Lee Harrison of the University of Pittsburgh School of Medicine, whose study appears in the New England Journal of Medicine, said in a statement.

“When vaccinated children don’t carry these virulent strains, they don’t end up transmitting them to other children, their parents and grandparents.”

Harrison said the study clearly shows adults not covered by the vaccine benefit, suggesting it conveys so-called “herd immunity” to people who have not been vaccinated. Previous studies showed it protected elderly people against deadly pneumonia strains, even when they were not given an adult vaccine.

Data has previously been mixed on whether Prevnar was reducing meningitis infections in adults.

“That is why we did the study,” Harrison said in a telephone interview. “It was a huge question because the death rate from pneumococcal meningitis is over 20 percent.”

Harrison’s team reviewed cases of pneumococcal meningitis from 1998 through 2005. They found disease rates fell 64 percent in children under 2 and 54 percent in older adults after the 2000 introduction of Prevnar, also known as Prevenar, pediatric pneumococcal conjugate vaccine or PCV7.

Prevnar protects against seven of the most common strains of Streptococcus pneumoniae, known commonly as pneumococcal bacteria. These germs account for more than 80 percent of pneumococcal disease in children, causing ear infections, meningitis, pneumonia and blood infections.

Harrison said non-PCV7 strains of meningitis increased by 60.5 percent from 1998-99 to 2004-2005. They also found the percentage of strains not sensitive to penicillin rose to 30.1 percent in 2005, from 19.4 percent in 2003. “The fact that these strains are increasing is obviously worrisome,” he said.

Harrison said the vaccine has been highly successful in preventing bacterial meningitis, but it remains deadly.

“We do need new vaccines that will cover additional strains not included in the current vaccine,” he said.

Wyeth is testing an expanded version of the vaccine that will cover 13 strains of pneumococcal bacteria and has said it plans to seek U.S. regulatory approval in the first quarter of this year.

Harrison said he evaluated the new Wyeth vaccine and based on currently available data, he thinks it will cover about half of the remaining disease.

CHICAGO (Reuters)