Biogen : to Webcast Prerecorded Encore Aducanumab Presentation and Live Q&A from AAN 2020 Science Highlights on September 23, 2020

Cambridge, Mass. - September 22, 2020 - Biogen (Nasdaq: BIIB) today announced it will host a prerecorded webcast of its encore presentation related to its Alzheimer's disease investigational therapy, aducanumab, as well as a live, virtual question and answer (Q&A) session at the upcoming AAN 2020 Science Highlights. All data in this presentation have been previously presented.

Webcast Details:

• Wednesday, September 23, 2020, 1:00 p.m. ET - Encore platform presentation and Q&A: EMERGE and ENGAGE Topline Results: Phase 3 Studies of Aducanumab in Early Alzheimer's Disease, Samantha Budd Haeberlein, Ph.D., Senior Vice President, Head Neurodegeneration Development Unit at Biogen, and Q&A with Carmen Castrillo-Viguera, M.D., Medical Director, Clinical Development at Biogen

To access the webcast and live Q&A session, please complete a free registration at the link here in advance of the meeting. To avoid any delay in viewing the webcast, please plan to register at least 10 minutes prior to the start of the webcast. Following the event, an archived version will be available on the Investors section of Biogen's website at investors.biogen.com.

About Biogen
At Biogen, our mission is clear: we are pioneers in neuroscience. Biogen discovers, develops and delivers worldwide innovative therapies for people living with serious neurological and neurodegenerative diseases as well as related therapeutic adjacencies. One of the world's first global biotechnology companies, Biogen was founded in 1978 by Charles Weissmann, Heinz Schaller, Kenneth Murray and Nobel Prize winners Walter Gilbert and Phillip Sharp. Today Biogen has the leading portfolio of medicines to treat multiple sclerosis, has introduced the first approved treatment for spinal muscular atrophy, commercializes biosimilars of advanced biologics and is focused on advancing research programs in multiple sclerosis and neuroimmunology, Alzheimer's disease and dementia, neuromuscular disorders, movement disorders, ophthalmology, immunology, neurocognitive disorders, acute neurology and pain.

We routinely post information that may be important to investors on our website at www.biogen.com. To learn more, please visit www.biogen.com and follow us on social media - Twitter, LinkedIn, Facebook,YouTube.

About Aducanumab
Aducanumab (BIIB037) is an investigational human monoclonal antibody studied for the treatment of early Alzheimer's disease. Biogen licensed aducanumab from Neurimmune under a collaborative development and license agreement. Since October 2017 Biogen and Eisai Co., Ltd. have collaborated on the development and commercialization of aducanumab globally.

EMERGE and ENGAGE were Phase 3 multicenter, randomized, double-blind, placebo-controlled, parallel-group studies designed to evaluate the efficacy and safety of aducanumab. The primary objective of the studies was to evaluate the efficacy of monthly doses of aducanumab as compared with placebo in reducing cognitive and functional impairment as measured by changes in the Clinical Dementia Rating-Sum of Boxes (CDR-SB) score. Secondary objectives were to assess the effect of monthly doses of aducanumab as compared to placebo on clinical decline as measured by the Mini-Mental State Examination (MMSE), the Alzheimer's Disease Assessment Scale-Cognitive Subscale 13 Items (ADAS-Cog 13), and the Alzheimer's Disease Cooperative Study-Activities of Daily Living Inventory Mild Cognitive Impairment Version (ADCS-ADL-MCI).

MEDIA CONTACT: David Caouette + 1 617 679 4945 [e-mail]

INVESTOR CONTACT: Joe Mara [phone] [e-mail]