Researchers have begun a major clinical trial in Africa of what could become the world's first vaccine against malaria, a disease that kills nearly a million people every year.

The vaccine's developers -- drug giant GlaxoSmithKline PLC and the Path Malaria Vaccine Initiative, or MVI, a charitable group funded by the Bill & Melinda Gates Foundation -- began a study in 16,000 African children this week, the largest-ever trial of the potential inoculation.

The...