OUR PURPOSE PIONEERING SCIENCE PATIENTS OUR PEOPLE ENVIRONMENT COMMUNITY REPORTING 6 BIOGEN 2021 YEAR IN REVIEW CEO LETTER My fellow stockholders, The year 2021 was an eventful one for Biogen and our portfolio, and one of continued execution across our base business. Neuroscience, Biogen’s principal area of focus, is an attractive field with great potential for innovation and scientific breakthroughs that address significant unmet needs of patients living with devastating diseases. Our emphasis on scientific advancements in service of humanity has driven our leadership in multiple sclerosis (MS), our innovation in spinal muscular atrophy (SMA), and our success in biosimilars. We also achieved important milestones, including: – FDA approval of ADUHELM (aducanumab-avwa), the first novel therapy approved for Alzheimer’s disease since 2003. – Important data readouts for potential treatments in depression, stroke, amyotrophic lateral sclerosis (ALS). – The formation of Biogen Digital Health, a global unit dedicated to pioneering personalized and digital medicine in neuroscience. To fully realize the significant opportunity we see ahead, we are pursuing a strategic plan that leverages our core competencies in neurology and in related growth areas. Alzheimer’s Disease Update In June 2021, the FDA granted accelerated approval to ADUHELM, the first treatment directed at an underlying pathophysiology of Alzheimer’s disease, the presence of amyloid beta plaques in the brain. ADUHELM’s introduction to the market proceeded more slowly than we would have hoped amid questions around the product’s mechanism of action and clinical data. In April 2022, we were disappointed that the U.S. Centers for Medicare & Medicaid Services (CMS) issued an unprecedented final coverage determination that effectively denies all Medicare beneficiaries access to ADUHELM. This ruling may also limit coverage for any future FDA-approved treatment in the class. Neuroscience, Biogen’s principal area of focus, is an attractive field with great potential for innovation and scientific breakthroughs that address significant unmet needs of patients living with devastating diseases.” Michel Vounatsos Chief Executive Officer