TYSABRI(R) Demonstrates Significant Health-Related Quality-of-Life Improvements for Multiple Sclerosis Patients in Study Published in Annals of Neurology

Biogen Idec (NASDAQ: BIIB) and Elan Corporation, plc (NYSE: ELN)
announced today the publication of results demonstrating that patients
treated with TYSABRI(R) (natalizumab) showed a significant improvement
in health-related quality-of-life (HRQoL) measures when compared to
placebo. These results are from the first Phase III multiple sclerosis
(MS) studies that have demonstrated improvement on HRQoL measures in
patients with relapsing forms of MS. The results have been published
in today's issue of Annals of Neurology.

"These data showed that patients treated with TYSABRI were more
likely to experience statistically important improvement in the
quality-of-life measures used to assess meaningful disease improvement
or progression. These findings have not been previously observed in
clinical studies involving MS patients," said Richard Rudick, MD,
Director of the Mellen Center for Multiple Sclerosis Treatment and
Research at the Cleveland Clinic, the lead investigator of the study.

These two-year, randomized, double-blind, placebo-controlled,
multicenter, Phase III clinical trials (AFFIRM and SENTINEL) were
conducted in 2,113 patients with relapsing forms of MS. The objective
was to assess the relationship between disease activity and HRQoL in
relapsing forms of MS, and the impact of TYSABRI on these measures.

In the studies, HRQoL was assessed using two different measures at
baseline and weeks 24, 52 and 104:

-- The Short Form-36 (SF-36), a standardized, well-validated
survey that has been used extensively in many disease areas,
including MS to review health status. The SF-36 is comprised
of 36 questions designed to assess physical (Physical
Component Summary or PCS) and mental (Mental Component Summary
or MCS) well-being from the perspective of the patient.

-- The Visual Analogue Scale (VAS), a measure of well-being as
assessed by the patient and marked on a scale of 0 to 100,
with 0 indicating "poor" and 100 indicating "excellent."

Results from the AFFIRM monotherapy trial include:

-- A statistically significant improvement in SF-36 PCS beginning
at week 24 and all subsequent time points compared with a
decline in the placebo-treated group.

-- A statistically significant improvement in SF-36 MCS at week
104 compared with a decline in the placebo-treated group.

-- Statistically significant benefits using the VAS when compared
with placebo at week 52 and at week 104.

-- Patients showed sustained improvement from baseline
quality-of-life measures, not just a slowing down of
quality-of-life deterioration.

-- HRQoL measures correlated with common measures of MS severity,
including EDSS, sustained disability progression, relapse
number, MSFC and volume of T2-hyperintense and T1-hypointense
lesions.

Improvements on quality-of-life measures were also observed in the
SENTINEL study, in which TYSABRI was added to AVONEX(R) (Interferon
beta-1a). This publication is in addition to a presentation of
preliminary results from the same study presented at the 2006 American
Academy of Neurology Annual Meeting.

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 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), infections, depression
and gallstones. 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 trials,
the incidence and rate of other serious and common adverse events,
including the overall incidence and rate of infections, were balanced
between treatment groups.

Common adverse events reported in TYSABRI-treated patients include
headache, fatigue, infusion reactions, urinary tract infections, joint
and limb pain, lower respiratory infections, rash, gastroenteritis,
abdominal discomfort, vaginitis, and diarrhea.

In addition to the United States and European Union, TYSABRI is
also approved in Switzerland, Canada, Australia and Israel. TYSABRI
was discovered by Elan and is co-developed with Biogen Idec.

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 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, or that the
companies may encounter other unexpected hurdles. 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.