"Last week dosing was restarted," Elan CEO Kelly Martin told analysts and money managers at the Goldman Sachs annual Global Healthcare Conference being held in Dana Point, California. He said the study, which had been suspended in mid-April, was "back on track."

The vaccine is designed to stimulate the immune system to block production of A-beta peptide, a component of the amyloid plaque that is believe to form tangles in the brain that cause Alzheimer's.

The suspension was meant to allow Elan and partner Wyeth (WYE.N: Quote, Profile, Research, Stock Buzz) to examine a potentially serious side effect suffered by one patient in the mid-stage trial. The patient was hospitalized with skin lesions that a lead researcher suspected was a case of vasculitis, an inflammation of blood vessels.

Elan and Wyeth are also co-developing another Alzheimer's drug, called AAB-001, that is farther along in testing and is considered by many analysts to be the most promising product in development against the degenerative brain disease. The compound recently began late-stage trials.