NEW YORK - Researchers reported promising results for what may become the world's first vaccine to prevent malaria, a killer of one million people each year.

In early tests, the experimental vaccine was more than 50 percent effective in preventing the deadly disease in infants and young children in Africa, the scientists said today. A larger and longer test is set to begin early next year.

It is the first malaria vaccine to make it this far, and if further studies are successful, marketing approval could be sought as early as 2011. The vaccine was developed by the British-based GlaxoSmithKline PLC (which has operations in the Philadelphia area).

The results "add to our confidence that we are closer than ever before" to a malaria vaccine for African children, Christian Loucq, director of the PATH Malaria Vaccine Initiative, said at a news conference.

The nonprofit group was established to help develop malaria vaccines and make sure they're available where needed. The group teamed up with GlaxoSmithKline, and both paid for the vaccine studies.

The findings were being presented today at a meeting of the American Society for Tropical Medicine and Hygiene in New Orleans and will be in Thursday's New England Journal of Medicine. Some of the researchers work for the nonprofit group or the drugmaker.

Malaria is a tropical disease whose victims are mostly young children in sub-Saharan Africa. It is caused by a parasite and spread through a bite from an infected mosquito. The parasite travels quickly to the liver, where it matures, enters the bloodstream, and causes fever, chills, flu-like symptoms and anemia.

The GlaxoSmithKline vaccine is designed to attack the parasite before it can infect the liver.