An experimental vaccine has proved 100 percent successful in preventing bacterial meningitis and severe bloodstream infections in children under the age of 5, researchers said Friday in San Diego.

The vaccine against pneumococcal disease proved so effective that researchers ended a three-year trial prematurely and immunized all of the 38,000 children being studied, a team from the Kaiser Permanente Vaccine Study Center in Oakland, Calif., told a meeting of the Interscience Conference on Antimicrobial Agents and Chemotherapy."This is a big win for children," added Dr. Jerome Klein of the Boston University School of Medicine, a leading expert on pneumococcal disease. "Meningitis will now become an uncommon disease." The vaccine could be widely available as early as sometime next year.

Currently, pneumococcal infections can be treated with antibiotics, but many infections are not caught in time to prevent complications. Physicians also fear that pneumococcus, like other bacteria, will become increasingly resistant to existing antibiotics.

In the United States, about 10,000 children develop pneumococcal infections each year, of which roughly 1,500 are meningitis - an inflammation of the brain and spinal cord - while the rest are blood infections. About 300 children a year die of meningitis. Many of those who survive lose their hearing, have seizures or incur developmental delays. World-wide, more than 1.2 million children die from pneumococcal infections.

"In my mind, this is the biggest vaccine breakthrough in the past eight to 10 years," said Dr. Henry Shinefield of the center, one of the co-leaders of the trial.

The team hopes the vaccine will also help protect against the 7 million ear infections each year caused by pneumococcal bacteria, but results from that portion of the study will not be available for another month.