For decades, scientists have known that they can make vaccines much more efficacious by adding aluminum compounds, but they never knew why. Now, a study reveals how, on a molecular level, these helpers spur the production of antibodies. The finding may help researchers develop better vaccines. Many vaccines contain adjuvants, nonspecific agents that help jolt the immune system into action. "Alum," a term referring broadly to aluminum hydroxide and several aluminum salts, has this effect, as was accidentally discovered in the 1920s. It has been widely used in human vaccines since the 1950s, and it's still the only adjuvant allowed...