New TYSABRI(R) Data to Be Presented at the European Committee for Treatment and Research in Multiple Sclerosis

Biogen Idec (NASDAQ: BIIB) and Elan Corporation, plc (NYSE: ELN)
announced that TYSABRI(R) (natalizumab) treatment significantly
increases the proportion of disease-free patients with multiple
sclerosis (MS) according to a post hoc analysis of the Phase III
AFFIRM study to be presented on Saturday, October 13, 2007 at the 23rd
Congress of the European Committee for Treatment and Research in
Multiple Sclerosis (ECTRIMS) in Prague, Czech Republic. Also to be
presented on Saturday will be findings from the PLEX study which
suggest that plasma exchange may be an effective means of accelerating
the removal of TYSABRI from the circulation.

Post Hoc Analysis of Phase III AFFIRM Study

The proportion of disease-free patients in the AFFIRM study was
determined based upon clinical and MRI criteria. The proportion of
disease-free patients 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 and no new or enlarging
T2-hyperintense lesions.

Using clinical and MRI disease-free criteria combined, the most
stringent definition of disease free, 36.7% of TYSABRI-treated
patients had no relapses, disability progression or MRI activity
compared with 7.2% of placebo patients (p<0.0001). In the clinical
analysis, 64.3% of TYSABRI-treated patients vs. 38.9% placebo-treated
patients(p<0.0001) were disease free or without relapses and
disability progression. Using MRI measures, 57.7% of TYSABRI-treated
patients vs. 14.2% placebo-treated patients (p<0.0001); were disease
free, or without gadolinium-enhancing lesions and new or enlarging
T2-hyperintense lesions.

"These data demonstrate the dramatic effect TYSABRI can have on
critical measures of multiple sclerosis. In addition to the impact on
individual clinical and MRI outcomes, it is striking that more than
one-third of patients were free of relapses, disability progression
and MRI activity after two years of treatment. This suggests that
TYSABRI may offer patients freedom from many of their MS symptoms,"
said Eva Havrdova, MD, PhD, Director of the Center for Demyelinating
Diseases at the First School of Medicine, General University Hospital,
Charles University, Prague, Czech Republic.

PLEX Plasma Exchange Study

Results from the PLEX study also to be presented suggest that
plasma exchange may be an effective means of accelerating the removal
of TYSABRI from blood serum. Plasma exchange is one of several
research efforts the companies have underway to learn more about
potential interventions or treatments for progressive multifocal
leukoencephalopathy (PML), a rare side effect of TYSABRI.

"These data from the PLEX study are encouraging as they show the
removal of TYSABRI is faster following plasma exchange. Time will tell
whether plasma exchange develops as an effective treatment approach
for PML," said Bhupendra O. Khatri, MD, Medical Director of the
Regional MS Center, Aurora St. Luke's Medical Center, Milwaukee, WI.

PLEX is an open-label, single-arm, multicenter exploratory study
involving 12 patients with relapsing-remitting MS designed to explore
whether plasma exchange could significantly reduce the concentration
of TYSABRI in blood serum and alpha 4-integrin receptor saturation.
Based on the PLEX findings, plasma exchange was effective at
accelerating the normal decline of serum TYSABRI concentrations.

Plasma exchange was generally well tolerated with no increase in
MS disease activity following plasma exchange. There were no study
discontinuations due to adverse events and all patients returned to
TYSABRI treatment without complications. Further investigations are
needed to determine whether plasma exchange holds promise as an
intervention in the setting of PML.

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) 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 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, and rash.

In addition to the United States and European Union, TYSABRI is
also approved in Switzerland, Canada, Australia, New Zealand 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 and the PLEX study. 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.