First Ten-Year Follow-Up Shows That Treatment with AVONEX ® Leads to Long-Term Benefits in Early Multiple Sclerosis Patients

SEATTLE, WA – April 30, 2009 – Biogen Idec (NASDAQ: BIIB) today announced data results from the CHAMPIONS ( C ontrolled H igh-Risk A VONEX ® (interferon beta-1a) M ultiple Sclerosis (MS) P revention Study I n O ngoing N eurologic S urveillance) study, an open label follow-up to CHAMPS ( C ontrolled H igh Risk Subjects A VONEX M S P revention S tudy). Based on the CHAMPS study, AVONEX was granted approval for use in patients who experienced their first clinical MS episode with MRI findings. The CHAMPIONS ten-year follow up showed that patients treated immediately after their first episode had significantly less chance of experiencing a second attack versus those patients with delayed treatment. These results at ten years also indicate that 80 percent of patients taking AVONEX were below an expanded disability status scale (EDSS) score of three. These data were presented as a poster at the Annual American Academy of Neurology (AAN) meeting.

"There is a consensus among physicians that early initiation of effective therapy beginning shortly after symptom onset may be required to alter the long term course of MS, but until now there has been little evidence to support this hypothesis,” said Dr. R. Philip Kinkel, director of the multiple sclerosis center, Beth Israel Deaconess Medical Center in Boston, MA and lead investigator of CHAMPIONS. “This data confirms that treatment of high risk patients beginning shortly after symptom-onset reduces relapse rates and may reduce disease progression for up to 10 years. This may translate into an ability to remain active and enjoy daily activities that otherwise might be lost without treatment."

The CHAMPIONS open label follow-up study was designed to determine long-term clinical outcomes and the ten-year follow up included 155 patients from 24 of the 50 Phase III CHAMPS study sites. Key findings include:

• 40 percent reduction in conversion to CDMS in patients treated immediately upon diagnosis of CIS versus those that were delayed by a median of 30 months (original placebo randomization arm)
• 91 percent of patients had an EDSS less than 4.0 after 10 years;
• 80 percent of patients on AVONEX had an EDSS of less than 3;
• the annualized relapse rate for patients with up to 10 years of care was only 0.25, suggesting a relapse rate of only one relapse every four years

“The CHAMPIONS study adds to the long-term follow-up data available and supports the benefits of starting early and staying on treatment with AVONEX,” said Thorsten Eickenhorst, M.D., vice president of global medical affairs, Biogen Idec . “This follow-up study conducted in MS patients who received early treatment reinforces the clinical effectiveness of AVONEX in patients who experience their first clinical MS episode.”

About AVONEX
AVONEX is the number one most prescribed treatment for relapsing forms of MS worldwide, with approximately 135,000 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 .

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Date Created: May 1, 2009