New One-Year Pharmacoeconomic Study Shows AVONEX(R) is Cost-Effective Relative to Other Interferon Therapies for Multiple Sclerosis

Biogen Idec Inc. (NASDAQ: BIIB) announced today that one-year data
presented at the Academy of Managed Care Pharmacy's (AMCP) 2007 Annual
Meeting show that AVONEX(R) (Interferon beta-1a) is a cost-effective
therapy in multiple sclerosis (MS) when compared to other interferon
beta treatments. Using a comprehensive analysis of medical and
pharmacy costs, the results of the research concluded that patients
treated with AVONEX, the most prescribed MS therapy worldwide, have
the lowest total one-year cost to a health plan when compared to other
interferon beta treatments.

Researchers analyzed 10,622 patients over one year to assess how
demographic, administrative and clinical variables affect MS costs and
utilization patterns and to examine the economic impact of treating
MS. The independent data contained in Multiple Sclerosis
Benchmarks(TM)(1), the retrospective, claims-based, observational
study, showed that patients treated with AVONEX had the lowest average
one-year cost compared to patients receiving other interferon beta
treatments. It has been estimated that the total annual economic
burden of MS in the United States exceeds $6.8 billion with a lifetime
cost of $2.2 million per patient.(2)

"MS is a disease that can have an impact beyond its debilitating
effect on patients," said Michael Pollock, Vice President, Global
Health Economics, Biogen Idec. "Cost-effectiveness is an increasingly
important factor in treating chronic diseases like MS. This study
shows that in addition to its clinical impact, AVONEX can also help to
substantially reduce the cost of care for patients living with this
disease, when compared to other interferon beta treatments."

The MS Benchmarks analysis showed the total costs over one-year to
MS patients on interferon beta therapy were: AVONEX, $19,896.15;
Rebif(R) (Interferon beta-1a) sc, $22,207.85; and Betaseron(R)
(Interferon beta-1b), $21,073.33.

In addition, AVONEX patients were more likely to refill their
prescriptions (avg.9.6/yr vs. 8.1 and 8.2/yr for other interferon beta
therapies) and were less likely to use certain concomitant
medications. Over the one-year period, use of disease-modifying
therapies (interferon beta and glatiramer acetate) was almost always
observed as monotherapy, reflecting little evidence of combination use
or switching between products.

Additionally, according to data from the Quality Assessment of
Multiple Sclerosis Therapy (QUASIMS) study presented at the AMCP
Conference, patients do not derive additional clinical benefit from
switching among interferon beta therapies. QUASIMS, an open-label,
retrospective, observational study conducted in 14 countries, analyzed
7,156 MS patients who had received two years of uninterrupted therapy
with interferon beta as initial therapy or follow-up therapy.

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 later in Europe for the treatment of relapsing
forms of MS to slow the progression of disability and reduce relapses.
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. Please see complete
prescribing information available at 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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(1) "Multiple Sclerosis Benchmarks" is a trademark of Managed Care
Measures, LLC.

(2) Coyle PK, Hartung HP. Use of interferon beta in multiple
sclerosis: rationale for early treatment and evidence for dose-and
frequency-dependent effects on clinical response. Multiple Sclerosis.
2002: 8:2-9.