In the United States malaria is a disease known mostly from textbooks, an occasional news item or depiction in a movie or documentary. In much of the world, however, malaria remains an ever-present scourge that sickens hundreds of millions and that kills about a million people annually. Given the ubiquity of the disease and its toll, any advance that holds some promise of reducing or eradicating the mosquito-borne affliction is certainly welcome. That event, it appears, might be at hand.

A vaccine currently being tested in children has produced mostly positive results. The inoculation seems to reduce the risk of infection by about half and the chance of getting the most deadly form of malaria by about a third. As vaccines go, that's not particularly high. Polio and measles vaccines, for example, approach 100 percent in effectiveness. Still, the rates reported in the malaria trials are encouraging.

Malaria infects about 500 million individuals, most of them youngsters, each year. About a million die. A reduction of a third or a half in those numbers would be a blessing in many places. Malaria is endemic in at least 90 countries, and present across 90 percent of Africa, where it accounts for about 60 percent of health clinic visits, about half of all hospitalizations and about 40 percent of all medical spending.

The vaccine is problematic for reasons other than efficiency. Initial tests suggest it may not confer long-range benefits and that periodic boosters may be required. There's some indication, too, that side effects -- fevers and seizures, particularly-- might be a problem. Even so, world health officials and scientists generally agree that the benefits seemingly conferred by the malaria vaccine are useful and that testing should continue.

More tests will take time and money. That's not peculiar to malaria studies, but to all new vaccines. Testing any vaccine in a large population is a complex undertaking that requires strict adherence to scientific protocols. The malaria vaccine tests do have extensive funding. GlaxoSmithKline, the pharmaceutical company, has invested $300 million in its development and pledges more. The Bill & Melinda Gates Foundation added $200 million. If the new vaccine's efficacy can be replicated in additional testing, that money will be proved a wise investment.

Celebrations, though, should wait. Even if the vaccine proves viable, malaria likely will remain a global health issue until the mostly poor countries where it is prevalent can develop systems to deliver vaccine and other treatments to both urban slums and rural areas. The promise of an effective vaccine, however, is reason for optimism in the fight against malaria.