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Biogen is one step closer to getting its experimental Alzheimer's drug approved for use in the United States.

Food and Drug Administration staff issued documents Wednesday, saying the drug, Aducanumab, has shown "exceptionally persuasive" evidence that it is effective.

The FDA staff review elevates the drug's chances of swift FDA approval, which could come as early as March.

If approved, the drug would be the first new treatment for Alzheimer's disease in decades and the first that appears to slow progression of the disease.

Shares of Biogen soared 43 percent on the FDA panel's findings. Other drugmakers with Alzheimer's drugs in development, such as Eli Lilly, rallied as well.