One of the most dramatic turnarounds in drug development history could be in sight after US drugmaker Biogen announced plans to seek regulatory approval of its first therapy to slow Alzheimer's disease on Tuesday.

About 10 million people in US might qualify for treatment if the drug, called Aducanumab, is approved by the Food and Drug Administration, said the company's chief executive.

The announcement is somewhat stunning as no drugs can do this - existing ones only help with symptoms. Thus, it has caused the company's share price to soar and taken Weibo by storm, being mentioned in thousands of posts.

A new analysis showed higher doses of the drug can offer significant benefit to people with early Alzheimer's, slowing their clinical decline so they preserve more of their memory and everyday living skills - things the disease usually robs.

Biogen also said it will file the paperwork in early 2020 and has its sights on Europe, too. Approval processes could take a year or two. If successful, the company aims to initially offer the drug to patients previously enrolled in clinical studies.