CORRECTING AND REPLACING Biogen Idec to Report Fourth Quarter and Year End 2014 Financial Results on January 29, 2015

Please replace the release with the following corrected version due to multiple revisions.

The corrected release reads:

BIOGEN IDEC TO REPORT FOURTH QUARTER AND YEAR END 2014 FINANCIAL RESULTS ON JANUARY 29, 2015

Biogen Idec Inc. (NASDAQ:BIIB) today announced that due to the severe blizzard that is expected to impact the Northeast through Wednesday morning, and the declared state of emergency, the Company has rescheduled its Fourth Quarter and Year End 2014 earnings release to Thursday, January 29, 2015, after the financial markets close.

Following the release of the financials, the Company will host a live webcast where Biogen Idec management will discuss the financial results, at 4:30 pm ET. To access the live webcast, please go to the investor relations section of Biogen Idec’s website at www.biogenidec.com. Following the live webcast, an archived version of the call will be available at the same URL, for one month.

About Biogen Idec

Through cutting-edge science and medicine, Biogen Idec discovers, develops and delivers to patients worldwide innovative therapies for the treatment of neurodegenerative diseases, hemophilia and autoimmune disorders. Founded in 1978, Biogen Idec is the world’s oldest independent biotechnology company. Patients worldwide benefit from its leading multiple sclerosis therapies. For product labeling, press releases and additional information about the company, please visit www.biogenidec.com.