A childhood vaccine approved in 2000 for use in the United States has started to ease a racial disparity that saw blacks more likely to fall victim to pneumonia and meningitis, according to a study published on Tuesday.

Incidence of the infection among U.S. black children younger than 2 went from being 3.3-times higher than among the country’s white youngsters before the vaccine, to 1.6 -times higher in 2002, the study said.

While the vaccine is a success among all races, the improvement in the U.S. black versus white rate probably reflects the fact that some black children were targeted for the immunization, the report from the Centers for Disease Control and Prevention in Atlanta said.

It may also be that so-called “herd immunity,” in which the vaccine protects even those not vaccinated by reducing the number of cases to which everyone is exposed-may be more effective in black communities for unexplained reasons, the authors added.

The report found that between 1998 and 2002, annual U.S. incidence of invasive pneumococcal disease-pneumonia and meningitis-decreased from 19 to 12.1 cases per 100,000 among whites and from 54.9 to 26.5 among blacks.

“Due to these declines, 14,730 fewer cases occurred among whites and 8,780 fewer cases occurred among blacks in the United States in 2002, compared with the average number in two pre-vaccine years, 1998 and 1999,” the study said.

“Before vaccine introduction, incidence among blacks was 2.9-times higher than among whites; in 2002, the black-white rate ratio had been reduced to 2.2,” it said.

Why blacks in the United States have suffered disproportionately from such diseases in the past is not known, the authors said.

The report, published in this week’s issue of the Journal of the American Medical Association, said the reductions were all the more remarkable because the vaccine, Prevnar, has been in short supply.

Wyeth is the sole manufacturer of the vaccine, which protects against several different strains of pneumococcal bacteria. Supply problems have continued, prompting the government earlier this year to tell doctors to temporarily cut back the vaccination schedule to two shots instead of four until things ease up.