OUR PURPOSE PIONEERING SCIENCE PATIENTS OUR PEOPLE ENVIRONMENT COMMUNITY REPORTING 23 ENHANCING OUR STRATEGIC PORTFOLIO BIOGEN 2021 YEAR IN REVIEW Amyotrophic Lateral Sclerosis (ALS) ALS is a fatal, progressive neurodegenerative disease that affects nerve cells, weakens muscles and severely compromises physical function. There are no genetically targeted treatment options for ALS. We are committed to advancing ALS research and have a broad pipeline of investigational drugs being evaluated. – We have been studying tofersen (BIIB067), an investigational antisense drug for superoxide dismutase 1 (SOD1), and along with Ionis Pharmaceuticals, we released topline results from our Phase 3 VALOR study in 2021. SOD1-ALS is a rare, genetic form of ALS that accounts for approximately 2% of the estimated 168,000 people who have the disease globally. While tofersen did not meet the primary endpoint in the VALOR study, trends favoring tofersen were seen across biologic activity and clinical function. In addition, a pre-specified integration of data from VALOR and its ongoing open-label extension study (OLE) reinforced these findings and showed that early tofersen initiation led to less decline across multiple measures of motor function, respiratory function, muscle strength and quality of life in people with SOD1-ALS. Based on the totality of these results, Biogen successfully opened an early access program (EAP) for tofersen. We are engaging with regulators, the medical community, patient advocacy groups and other key stakeholders around the world to determine potential next steps. Read more results from the Phase 3 VALOR study. – In early 2022, we discontinued our clinical program of BIIB078, an investigational antisense oligonucleotide for C9orf72-associated ALS, which we were pursuing with Ionis Pharmaceuticals, Inc. The therapy did not meet any secondary efficacy endpoints, and it did not demonstrate clinical benefit. With Ionis, we remain committed to our decade-long pursuit of advancing ALS research and developing therapies. Þ READ MORE ABOUT OUR DECISION RELATED TO BIIB078 Þ READ ABOUT HOW BIOGEN IS SUPPORTING HEALTH ACCESS FOR PEOPLE WITH A DIAGNOSIS OR FAMILY HISTORY OF ALS SPOTLIGHT ALS Identified™ offers free access to genetic testing Early genetic testing, diagnosis and interventions are critical to the health of ALS patients. With this in focus, Biogen is sponsoring ALS Identified, a program that facilitates access to genetic testing at no charge to patients. Offered through Invitae, the program is open to anyone 18 years or older within the U.S. and Puerto Rico with a diagnosis or a family history of ALS. Since ALS Identified launched in June 2021, more than 400 physicians and 3,000 people have participated. ALS Identified offers testing with the Invitae Amyotrophic Lateral Sclerosis Panel, which includes more than 20 ALS-associated genes. An optional add-on preliminary-evidence gene panel includes additional genes that do not currently have a definitive clinical association with ALS, but may prove to be clinically significant in the future. ALS Identified can help patients and their families understand their disease or risk and consider opportunities to participate in genetic ALS research. It also equips doctors with information and resources and aims to advance research into genetic ALS. De- identified data will be shared with patient advocacy groups and key medical experts to foster research and improve knowledge of the disease. In the future, we plan to expand the program to additional countries with high barriers to genetic testing. Þ LEARN MORE ABOUT ALS IDENTIFIED Cells expressing a protein found in ALS.