New Long-Term Data Show That Patients Taking AVONEX(R) for up to 15 Years Experience Reduced Disability Progression and Improved Quality of Life.

MONTREAL -- Biogen Idec (NASDAQ: BIIB) today announced that data was presented from the ASSURANCE (ASSessment of Drug Utilization, EaRly TreAtmeNt, and Clinical OutcomEs) study, showing the long-term benefits of AVONEX([R]) (interferon beta-1a IM) therapy in patients with relapsing multiple sclerosis (MS) for up to 15 years. The ASSURANCE study represents the long-term follow-up of patients who participated in the Multiple Sclerosis Collaborative Research Group (MSCRG), the original Phase III pivotal trial from which AVONEX was approved. Data from this study were presented today as a poster presentation at the World Congress on Treatment and Research in Multiple Sclerosis in Montreal, Canada. This is the first joint meeting of the Americas Committee on Treatment and Research in Multiple Sclerosis (ACTRIMS) and its counterparts in Europe and Latin America: ECTRIMS and LACTRIMS.

"As a physician, my goal in treating my MS patients is to delay disability progression and help them maintain their normal lifestyle for as long as possible," said Robert Bermel, MD, Mellen Center for Multiple Sclerosis Treatment and Research, Cleveland Clinic. "This follow-up study identifies a group of patients who achieved benefits from long-term treatment, and underscores the importance of starting on and continuing an effective therapy for MS."

The data from the study show that patients currently taking AVONEX for up to 15 years (range of 3 - 15 years) versus those not on AVONEX therapy reported:

* Significantly lower disability progression as measured by a mean change in Expanded Disability Scale Scores (EDSS) of 2.3 vs. 3.3 (p=0.011) from MSCRG baseline;

* Lower disability progression to EDSS milestones four (64% vs. 83%, p=0.06), six (32% vs. 62%, p=0.008) and seven (9% vs. 33%, p=0.008);

* Greater quality of life as measured by the physical component score of the SF-36 (p<0.0001);

* Significantly greater sense of independence in self care (p=0.0019); and

* Significantly more independent living (p=0.031).

ASSURANCE was an open-label, retrospective, patient-reported, multicenter, 15-year follow-up study that included patients with relapsing MS who received 2 years of treatment in the pivotal Phase III trial (n=172). One hundred thirty-six of a possible 172 patients enrolled in the study. Patients were categorized as current AVONEX users and non-AVONEX users. Forty-six percent of those patients were currently taking AVONEX, with median treatment duration of 13.3 years. Patients not currently on AVONEX were treated with a number of other disease-modifying therapies, with 24 percent of patients undergoing treatment with TYSABRI([R]) (natalizumab).

"This level of impact on disability and quality of life over the course of 15 years reinforces the real-life benefits and proven clinical effectiveness of AVONEX," said Thorsten Eickenhorst, MD, Vice President of Global Medical Affairs, Biogen Idec. "We pride ourselves on providing a treatment that is not only efficacious now but will continue to offer patients the support they need for as long as possible."

About AVONEX

AVONEX is the most prescribed treatment for relapsing forms of MS worldwide, with more than 130,000 patients on therapy. It was launched in the U.S. in 1996 and in Europe in 1997 for the treatment of relapsing forms of MS to slow the progression of disability and reduce relapses. AVONEX has been proven effective in clinical trials for up to three years. AVONEX is marketed internationally in more than 90 countries. AVONEX was the first treatment approved for patients who have their first clinical MS attack and have a brain MRI scan consistent with MS; this use was approved in Europe in 2002 and in the U.S. in 2003.

The most common side effects associated with AVONEX multiple sclerosis treatment are flu-like symptoms, including myalgia, fever, fatigue, headache, chills, nausea, vomiting, pain, and asthenia.

AVONEX should be used with caution in patients with depression or other mood disorders and in patients with seizure disorders. AVONEX should not be used by pregnant women. Patients with cardiac disease should be closely monitored. Patients should also be monitored for signs of hepatic injury. Routine periodic blood chemistry and hematology tests are recommended during treatment with AVONEX. Rare cases of anaphylaxis have been reported. For more information, visit www.AVONEX.com

About Biogen Idec

Biogen Idec creates new standards of care in therapeutic areas with high unmet medical needs. Founded in 1978, Biogen Idec is a global leader in the discovery, development, manufacturing, and commercialization of innovative therapies. Patients in more than 90 countries benefit from Biogen Idec's significant products that address diseases such as lymphoma, multiple sclerosis, and rheumatoid arthritis. For product labeling, press releases and additional information about the company, please visit www.biogenidec.com.