Biogen Idec and Elan Present New TYSABRI(R) Data at the 60th Annual Meeting of the American Academy of Neurology

Biogen Idec (NASDAQ: BIIB) and Elan Corporation, plc (NYSE: ELN)
today announced new data on the global utilization, safety and overall
patient exposure of TYSABRI(R) (natalizumab). As of the end of March
2008, approximately 26,000 patients were on commercial and clinical
therapy worldwide with no cases of progressive multifocal
leukoencephalopathy (PML) reported since re-launch in the U.S. and
launch internationally in July 2006. Growth in global utilization plus
increasing confidence in the favorable benefit-risk profile of TYSABRI
indicate the companies are making great progress toward the goal of
100,000 patients on therapy by year-end 2010. These data were
presented today at the 60th Annual Meeting of the American Academy of
Neurology (AAN).

"These data suggest that neurologists and patients are
increasingly choosing TYSABRI for the treatment of their disease. The
significant clinical benefits are established and TYSABRI continues to
offer the potential for compelling efficacy and hope for those
patients living with MS," said Michael Panzara, MD, MPH, Vice
President and Chief Medical Officer, Neurology Strategic Business
Unit, Biogen Idec.

"Positive outcomes for patients continue to support TYSABRI´s
strength as a valuable treatment for multiple sclerosis patients in
more than 30 countries around the world. We are also excited that
patients with Crohn´s Disease are now enrolling in the TOUCH program
and beginning to receive TYSABRI treatment in the U.S.," said Gordon
Francis, MD, Senior Vice President, Global Clinical Development, Elan.

According to data available as of the end of March 2008:

-- In the U.S., approximately 15,300 patients were on TYSABRI

therapy commercially and approximately 2,750 physicians have

prescribed the therapy;

-- Outside of the U.S., more than 10,200 patients were on TYSABRI

therapy commercially;

-- In global clinical trials, more than 600 patients were on

TYSABRI therapy; and

-- There have been no cases of PML since re-launch in the US and

launch internationally in July 2006.

Cumulatively, in the combined clinical trial and post-marketing
settings:

-- More than 36,700 patients have been treated with TYSABRI; and

-- Of those patients, over 9,900 have received at least one year

of TYSABRI therapy and more than 3,600 patients have been on

therapy for 18 months or longer.

TYSABRI is available in the U.S. through the TOUCH(TM) Prescribing
Program. All U.S. prescribers, infusion sites, and patients receiving
TYSABRI are required to enroll in TOUCH. Safety information is also
collected through ongoing clinical trials and registries, including
TYGRIS and the pregnancy registry, making this the largest long-term
patient follow-up effort undertaken for any MS therapy.

The abstract for this study, "Natalizumab Utilization and Safety
in Patients with Relapsing Multiple Sclerosis: Updated Results from
TOUCH(TM) and TYGRIS" (Presentation #S02.002), is available online at
the AAN´s Web site.

TYSABRI Increases the Proportion of MS Patients Considered Disease
Free

Biogen Idec and Elan also announced today at the meeting that
TYSABRI treatment significantly increases the proportion of patients
with MS considered to be disease free, according to post-hoc analyses
of the AFFIRM and SENTINEL clinical trials. The proportion of patients
considered disease free in the studies was determined based upon both
clinical and MRI criteria. In the studies, the proportion of patients
considered disease free over two years was significantly higher in the
TYSABRI-treated group compared with the placebo group, regardless of
how disease free was defined.

Clinically, disease free was defined as no relapses and no
progression of disability (as defined by > or =1.0-point increase in
Expanded Disability Status Scale (EDSS) score from a baseline score of
> or =1.0, or a > or =1.5-point increase from a baseline score of 0.0

sustained for 12 weeks) over two years. MRI disease free was defined
as no gadolinium-enhancing lesions seen on annual MRI scans and no new
or enlarging T2-hyperintense lesions over two years.

"The ultimate goal of an MS treatment is to help patients remain
symptom free for as long as possible. These data show natalizumab may
do just that as about one-third of patients were shown to have no
relapses, no disability progression and no new MRI markers. This is
further evidence that treatment with natalizumab can result in truly
dramatic outcomes for a large group of patients," said the study´s
lead author, Steven Galetta, MD, Professor of Neurology, University of
Pennsylvania School of Medicine.

In the AFFIRM trial, patients were randomized to receive TYSABRI
or placebo, while in the SENTINEL trial, randomized patients received
TYSABRI plus interferon beta-1a or placebo plus interferon beta-1a.
Over a two-year period, patients were evaluated utilizing clinical
criteria, MRI criteria and combined criteria with both trials
demonstrating TYSABRI treatment significantly increased the
proportions of patients considered disease free. Using clinical and
MRI disease-free criteria combined, a stringent definition of disease
free, 36.7% and 31.7% of patients in the TYSABRI groups were disease
free compared with 7.2% and 10.9% given placebo in the AFFIRM and
SENTINEL trials, respectively. By individual criteria, TYSABRI benefit
was also demonstrated using clinical (AFFIRM: 64.3% vs. 38.9%;
SENTINEL: 47.4% vs. 28.0%) and MRI definitions of disease free
(AFFIRM: 57.7% vs. 14.2%; SENTINEL: 65.5% vs. 27.6%). In both studies

results were similar in patients with highly-active and non-highly
active MS.

The abstract for this study, "Natalizumab Increases the Proportion
of Patients Free of Clinical or MRI Disease Activity in Relapsing
Multiple Sclerosis" (Poster #P02.156), is available online at the
AAN´s Web site.

About TOUCH(TM) and TYGRIS

Before initiating treatment, all U.S. patients, prescribers and
infusion sites must be enrolled in the TOUCH Prescribing Program
(TYSABRI Outreach: Unified Commitment to Health). TOUCH is designed to
determine the incidence of and risk factors for serious opportunistic
infections (OIs), including PML, and to monitor patients for signs and
symptoms of PML while promoting informed benefit-risk discussions
prior to initiating TYSABRI treatment. Physicians report on PML, other
serious OIs, deaths and discontinuation of therapy on an ongoing
basis.

TYGRIS (TYSABRI Global ObseRvation Program In Safety) is expected
to enroll 5,000 patients worldwide, including approximately 2,000 -
2,500 patients from TOUCH. Patients in TYGRIS are evaluated at
baseline and every six months thereafter for five years. Researchers
will evaluate data including medical/MS history; prior TYSABRI use;
prior use of immunomodulatory, antineoplastic, or immunosuppressive
agents; and all serious adverse events, including PML and other
serious OIs and malignancies.

Adverse event reporting in the post-marketing setting is
voluntary. It is possible that not all reactions have been reported

or that some reactions are not reported to Biogen Idec or Elan in a
timely manner.

About TYSABRI

TYSABRI is a treatment approved for relapsing forms of MS in the
United States and relapsing-remitting MS in the European Union.
According to data that have been published in the New England Journal
of Medicine, after two years, TYSABRI treatment led to a 68% relative
reduction (p<0.001) in the annualized relapse rate compared to placebo
and reduced the relative risk of disability progression by 42-54%
(p<0.001).

TYSABRI was recently approved to induce and maintain clinical
response and remission in adult patients with moderately to severely
active Crohn´s disease (CD) with evidence of inflammation who have had
an inadequate response to, or are unable to tolerate, conventional CD
therapies and inhibitors of TNF-alpha.

TYSABRI increases the risk of progressive multifocal
leukoencephalopathy (PML), an opportunistic viral infection of the
brain that usually leads to death or severe disability. Other serious
adverse events that have occurred in TYSABRI-treated patients included
hypersensitivity reactions (e.g., anaphylaxis) and infections. Serious
opportunistic and other atypical infections have been observed in
TYSABRI-treated patients, some of whom were receiving concurrent
immunosuppressants. Herpes infections were slightly more common in
patients treated with TYSABRI. In MS and CD clinical trials, the
incidence and rate of other serious adverse events, including serious
infections, were similar in patients receiving TYSABRI and those
receiving placebo. Common adverse events reported in TYSABRI-treated
MS patients include headache, fatigue, infusion reactions, urinary
tract infections, joint and limb pain and rash. Other common adverse
events reported in TYSABRI-treated CD patients include respiratory
tract infections and nausea. Clinically significant liver injury has
been reported in patients treated with TYSABRI in the post-marketing
setting.

TYSABRI is approved in more than 30 countries including the United
States and many countries throughout the European Union, as well as
Switzerland, Canada, Australia, New Zealand and Israel.

For more information about TYSABRI please visit www.tysabri.com

www.biogenidec.com or www.elan.com or call 1-800-456-2255.

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.

About Elan

Elan Corporation, plc is a neuroscience-based biotechnology
company committed to making a difference in the lives of patients and
their families by dedicating itself to bringing innovations in science
to fill significant unmet medical needs that continue to exist around
the world. Elan shares trade on the New York, London and Dublin Stock
Exchanges. For additional information about the company, please visit
www.elan.com.

Safe Harbor/Forward-Looking Statements

This press release contains forward-looking statements regarding
TYSABRI. These statements are based on the companies´ current beliefs
and expectations. The commercial potential of TYSABRI is subject to a
number of risks and uncertainties. Factors which could cause actual
results to differ materially from the companies´ current expectations
include the risk that we may be unable to adequately address concerns
or questions raised by the FDA or other regulatory authorities, that
concerns may arise from additional data, that the incidence and/or
risk of PML or other opportunistic infections in patients treated with
TYSABRI may be higher than observed in clinical trials, that the
companies may encounter other unexpected hurdles, or that new
therapies for MS with better efficacy or safety profiles or more
convenient methods of administration are introduced into the market.
Drug development and commercialization involves a high degree of risk.

For more detailed information on the risks and uncertainties
associated with the companies´ drug development and other activities

see the periodic and current reports that Biogen Idec and Elan have
filed with the Securities and Exchange Commission. The companies
assume no obligation to update any forward-looking statements, whether
as a result of new information, future events or otherwise.

Biogen Idec Important Information

Biogen Idec and its directors, executive officers and other
members of its management and employees may be deemed to be
participants in the solicitation of proxies from the stockholders of
Biogen Idec in connection with the Company´s 2008 annual meeting of
stockholders. Information concerning the interests of participants in
the solicitation of proxies will be included in any proxy statement
filed by Biogen Idec in connection with the Company´s 2008 annual
meeting of stockholders. In addition, Biogen Idec files annual

quarterly and special reports with the Securities and Exchange
Commission (the "SEC"). The proxy statements and other reports, when
available, can be obtained free of charge at the SEC´s web site at
www.sec.gov or from Biogen Idec at www.biogenidec.com. Biogen Idec
stockholders are advised to read carefully any proxy statement filed
in connection with the Company´s 2008 annual meeting of stockholders
when it becomes available before making any voting or investment
decision. The Company´s proxy statement will also be available for
free by writing to Biogen Idec Inc., 14 Cambridge Center, Cambridge

MA 02142. In addition, copies of the proxy materials may be requested
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telephone at (877) 750-5836 or by e-mail at info@innisfreema.com.