Other Financial Highlights

BIOGEN REPORTS Q1 2020 REVENUES OF $3.5 BILLION

GAAP diluted EPS increased 13%; Non-GAAP diluted EPS increased 31%

Biogen has open BLA and has started to submit modules, expects to complete the U.S. filing for aducanumab in third quarter

Biogen initiated re-dosing study for aducanumab and higher dose study for SPINRAZA

Biogen entered collaboration with Sangamo Therapeutics for gene regulation therapies for neurological disease

Cambridge, Mass., April 22, 2020 -- Biogen Inc. (Nasdaq: BIIB) today reported first quarter 2020 financial results.

"The COVID-19 pandemic has created a challenging situation for people and companies throughout the world, and Biogen personally felt the painful impact of this global crisis. During these challenging and unprecedented times, Biogen has continued to deliver on its mission and purpose," said Michel Vounatsos, Biogen's Chief Executive Officer. "We have continued to operate our business and deliver our therapies to patients across the world and are especially grateful to our dedicated employees as we continue to execute on our strategy."

Mr. Vounatsos added, "We delivered strong financial results in the first quarter, and we continued to develop and expand our pipeline, including making good progress toward the U.S. regulatory filing for aducanumab, as well as bolstering our efforts in gene therapy through a collaboration with Sangamo. The magnitude and uncertainty surrounding this pandemic clearly introduce unanticipated and potentially unquantifiable risks to our business and results over the near-term. That said, we believe that compelling opportunities exist in the therapeutic areas we are pursuing. This crisis has had a profound impact on our organization and the world at large. We have taken a broad set of actions, and we will remain fully engaged."

A reconciliation of GAAP to Non-GAAP quarterly financial results can be found in Table 3 at the end of this news release.

Biogen provided the following update regarding aducanumab, an anti-amyloid beta antibody candidate for the potential treatment of Alzheimer's disease that Biogen is developing in collaboration with Eisai Co., Ltd.:

Other Financial Highlights

Biogen's Response to COVID-19

To help ensure the health and safety of all stakeholders and society, Biogen has taken several actions in response to the ongoing COVID-19 pandemic, including:

Potential Business Impacts of COVID-19

Biogen has continued to operate its business to serve the needs of patients and has been continually monitoring for potential impacts:

Conference Call and Webcast

The Company's earnings conference call for the first quarter will be broadcast via the internet at 8:00 a.m. ET on April 22, 2020, and will be accessible through the Investors section of Biogen's website, www.biogen.com. Supplemental information in the form of a slide presentation is also accessible at the same location on the internet and will be subsequently available on the website for at least one month.

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.

This news release contains forward-looking statements, including statements made pursuant to the safe harbor provisions of the Private Securities Litigation Reform Act of 1995, relating to: our strategy and plans; potential of our commercial business and pipeline programs; capital allocation and investment strategy; clinical development programs, clinical trials, and data readouts and presentations; risks and uncertainties associated with drug development and commercialization; regulatory filings and the timing thereof; the potential benefits, safety, and efficacy of our products and investigational therapies; the anticipated benefits and potential of investments, collaborations, and business development activities; our future financial and operating results; and the direct and indirect impact of COVID-19 on our business and operations, including sales, expenses, supply chain, manufacturing, research and development costs, clinical trials, and employees. These forward-looking statements may be accompanied by such words as "aim," "anticipate," "believe," "could," "estimate," "expect," "forecast," "goal," "intend," "may," "plan," "potential," "possible," "will," "would," and other words and terms of similar meaning. Drug development and commercialization involve a high degree of risk, and only a small number of research and development programs result in commercialization of a product. Results in early stage clinical trials may not be indicative of full results or results from later stage or larger scale clinical trials and do not ensure regulatory approval. You should not place undue reliance on these statements or the scientific data presented.

These statements involve risks and uncertainties that could cause actual results to differ materially from those reflected in such statements, including: our dependence on sales from our products; failure to protect and enforce our data, intellectual property, and other proprietary rights and the risks and uncertainties relating to intellectual property claims and challenges; the direct and indirect impacts of the ongoing COVID-19 pandemic on our business, results of operations, and financial condition; uncertainty of long-term success in developing, licensing, or acquiring other product candidates or additional indications for existing products; failure to compete effectively due to significant product competition in the markets for our products; failure to successfully execute or realize the anticipated benefits of our strategic and growth initiatives; the risk that positive results in a clinical trial may not be replicated in subsequent or

confirmatory trials or success in early stage clinical trials may not be predictive of results in later stage or large scale clinical trials or trials in other potential indications; risks associated with clinical trials, including our ability to adequately manage clinical activities, unexpected concerns that may arise from additional data or analysis obtained during clinical trials, regulatory authorities may require additional information or further studies, or may fail to approve or may delay approval of our drug candidates; the occurrence of adverse safety events, restrictions on use with our products, or product liability claims; difficulties in obtaining and maintaining adequate coverage, pricing, and reimbursement for our products; risks relating to technology failures or breaches; our dependence on collaborators, joint venture partners, and other third parties for the development, regulatory approval, and commercialization of products and other aspects of our business, which are outside of our full control; risks associated with current and potential future healthcare reforms; risks relating to management and key personnel changes, including attracting and retaining key personnel; failure to comply with legal and regulatory requirements; the risks of doing business internationally, including currency exchange rate fluctuations; risks relating to investment in our manufacturing capacity; problems with our manufacturing processes; risks related to commercialization of biosimilars; fluctuations in our operating results; fluctuations in our effective tax rate; risks related to investment in properties; the market, interest, and credit risks associated with our portfolio of marketable securities; risks relating to share repurchase programs; risks relating to access to capital and credit markets; risks related to indebtedness; environmental risks; risks relating to the distribution and sale by third parties of counterfeit or unfit versions of our products; risks relating to the use of social media for our business; change in control provisions in certain of our collaboration agreements; and the other risks and uncertainties that are described in the Risk Factors section of our most recent annual or quarterly report and in other reports we have filed with the U.S. Securities and Exchange Commission.

These statements are based on our current beliefs and expectations and speak only as of the date of this news release. We do not undertake any obligation to publicly update any forward-looking statements.

Biogen Media Contact: Biogen Investor Contact:

David Caouette Joe Mara

Biogen Inc. Biogen Inc.

Tel: (781) 464-3260 Tel: (781) 464-2442

BIOGEN INC. AND SUBSIDIARIES

CONDENSED CONSOLIDATED STATEMENT OF INCOME

(unaudited, in millions, except per share amounts)

BIOGEN INC. AND SUBSIDIARIES

CONDENSED CONSOLIDATED BALANCE SHEETS

(unaudited, in millions)

BIOGEN INC. AND SUBSIDIARIES

GAAP TO NON-GAAP RECONCILIATION:

NET INCOME ATTRIBUTABLE TO BIOGEN INC. AND DILUTED EARNINGS PER SHARE

(unaudited, in millions, except per share amounts)

An itemized reconciliation between diluted earnings per share on a GAAP and Non-GAAP basis is as follows:

An itemized reconciliation between net income attributable to Biogen Inc. on a GAAP and Non-GAAP basis is as follows:

Notes to GAAP to Non-GAAP Reconciliation

A Amortization and impairment of acquired intangible assets for the three months ended March 31, 2020, compared to the prior periods, increased primarily due to a net overall increase in our expected rate of amortization for acquired intangible assets.

B In March 2019 we entered into a share purchase agreement with FUJIFILM Corporation (FUJIFILM) to sell all of the outstanding shares of our subsidiary that owned our biologics manufacturing operations in Hiller d, Denmark. The transaction closed in August 2019.

In the first quarter of 2019 we recorded a loss of approximately $174.6 million in our condensed consolidated statements of income. This estimated loss, which was subsequently remeasured each reporting period, included a pre-tax loss of $115.5 million reflecting our estimated fair value of the assets and liabilities held for sale as of March 31, 2019, adjusted for our expected costs to sell our Hiller d, Denmark manufacturing operations of approximately $10.0 million and includes our initial estimate of the fair value of an adverse commitment of approximately $120.0 million associated with the guarantee of future minimum batch production at the Hiller d facility. The value of this adverse commitment was determined using a probability-weighted estimate of future manufacturing activity. In addition, we recorded a tax expense of $59.1 million related to the planned transaction in the first quarter of 2019.

In August 2019 this transaction closed and we received approximately $881.9 million in cash, which may be adjusted based on contractual terms, which are discussed below. We determined that the operations disposed of in this transaction did not meet the criteria to be classified as discontinued operations under the applicable guidance.

During the fourth quarter of 2019 we recorded a $40.2 million reduction in our estimate of the future minimum batch commitment utilizing our revised manufacturing forecast, which reflects the impact of forecasted batches of aducanumab, an anti-amyloid beta antibody candidate for the potential treatment of AD that we are developing in collaboration with Eisai Co., Ltd., resulting in a reduction in the pre-tax loss on divestiture to $55.3 million for 2019. Our estimate of the adverse commitment obligation is approximately $74.0 million as of March 31, 2020 and December 31, 2019. We developed this estimate using a probability-weighted estimate of future manufacturing activity and may adjust this estimate based upon changes in business conditions, which may result in the increase or reduction of this adverse commitment obligation in subsequent periods. We also may be obligated to indemnify FUJIFILM for liabilities that existed relating to certain business activities incurred prior to the closing of this transaction.

In addition, we may earn certain contingent payments based on future manufacturing activities at the Hiller d facility. For the disposition of a business, our policy is to recognize contingent consideration when the consideration is realizable. Consistent with our assessment as of the transaction date, we currently believe the probability of earning these payments is remote and therefore we did not include these contingent payments in our calculation of the fair value of the operations

C 2017 corporate strategy implementation and restructuring charges are related to our efforts to create a leaner and simpler operating model.

D Amortization included in equity in loss of investee, net of tax represents the amortization of the differences between the fair value of our investment in Samsung Bioepis Co., Ltd. and the carrying value of our interest in the underlying net assets of the investee. These basis differences are amortized over their economic life.

Use of Non-GAAP Financial Measures

We supplement our consolidated financial statements presented on a GAAP basis by providing additional measures which may be considered "Non-GAAP" financial measures under applicable SEC rules. We believe that the disclosure of these Non-GAAP financial measures provides additional insight into the ongoing economics of our business and reflects how we manage our business internally, set operational goals and form the basis of our management incentive programs. These Non-GAAP financial measures are not in accordance with generally accepted accounting principles in the United States and should not be viewed in isolation or as a substitute for reported, or GAAP, net income attributable to Biogen Inc. and diluted earnings per share.

Our "Non-GAAP net income attributable to Biogen Inc." and "Non-GAAP earnings per share - Diluted" financial measures exclude the following items from "GAAP net income attributable to Biogen Inc." and "GAAP earnings per share - Diluted":

1. Acquisition and divestiture related costs

We exclude transaction, integration and certain other costs related to the acquisition and divestiture of businesses. We exclude certain purchase accounting related items associated with the acquisition of assets and amounts in relation to the consolidation or deconsolidation of variable interest entities. These adjustments include, but are not limited to, charges for in-process research and development and certain milestones, the amortization and impairment of intangible assets, charges or credits from the fair value remeasurement of our contingent consideration obligations and losses on assets and liabilities held for sale.

2. Restructuring, business transformation and other cost saving initiatives

We exclude costs associated with our execution of certain strategies and initiatives to streamline operations, achieve targeted cost reductions, rationalize manufacturing facilities or refocus research and development activities. These costs may include employee separation costs, retention bonuses, facility closing and exit costs, asset impairment charges or additional depreciation when the expected useful life of certain assets have been shortened due to changes in anticipated usage and other costs or credits that management believes do not have a direct correlation to our ongoing or future business operations.

3. (Gain) loss on equity security investments

We exclude unrealized and realized gains and losses and discounts or premiums on our equity security investments as we do not believe that these components of income or expense have a direct correlation to our ongoing or future business operations.

We evaluate other items of income and expense on an individual basis and consider both the quantitative and qualitative aspects of the item, including (i) its size and nature, (ii) whether or not it relates to our ongoing business operations and (iii) whether or not we expect it to occur as part of our normal business on a regular basis. We also include an adjustment to reflect the related tax effect of all reconciling items within our reconciliation of our GAAP to Non-GAAP net income attributable to Biogen Inc. and earnings per share - diluted.

BIOGEN INC. AND SUBSIDIARIES

(unaudited, in millions)

*Fumarate includes TECFIDERA and VUMERITY. VUMERITY became available in the U.S. in November 2019.

**Interferon includes AVONEX and PLEGRIDY.