New Pharmacoeconomic Data on TYSABRI(R) Demonstrate Significant Reduction in Steroid Use and Hospitalizations in Patients with Multiple Sclerosis

Biogen Idec (NASDAQ: BIIB) and Elan Corporation, plc (NYSE: ELN)
announced that data to be presented today at the Academy of Managed
Care Pharmacy's (AMCP) 2006 Educational Conference in Chicago, IL show
that in Phase III studies TYSABRI(R) (natalizumab) therapy
significantly reduced corticosteroid use and hospitalizations, and
increased the proportion of MS patients with no disease activity.
Findings will also be presented that demonstrate the positive impact
of TYSABRI on a number of health-related quality of life of measures
(QoL) and the cost-effectiveness of MS therapies.

Data Demonstrate TYSABRI Reduced Corticosteroid Use,
Hospitalizations and Increases the Proportion of Disease-Free Patients

Data presented today from the AFFIRM monotherapy study (two-year,
randomized, multi-center, placebo-controlled, double-blind study of
942 patients conducted in 99 sites worldwide), showed the impact of
TYSABRI on two pre-specified endpoints, the annualized rate of
relapses requiring corticosteroid use and the annualized rate of
hospitalizations due to MS. Data showed there was a 69% relative
reduction in the annualized rate of relapses requiring steroids for
patients treated with TYSABRI compared to those treated with placebo
(0.133 in the TYSABRI group vs. 0.432 in the placebo group(p<0.001)).
The study also showed that TYSABRI therapy resulted in a 65% relative
reduction in the annualized rate of MS-related hospitalizations over
two years (0.034 in the TYSABRI group vs. 0.097 in the placebo
group(p<0.001)).

A post-hoc analysis was also conducted to determine the proportion
of patients free of disease activity over two years. To determine
this, a retrospective analysis was conducted to evaluate both clinical
and magnetic resonance imaging (MRI) measures. Patients with no
disease activity were defined as patients who experienced no
additional relapses or progression of physical disability and
exhibited stable MRI measures without any new gadolinium-enhancing,
T2-hyperintense, or T1-hypointense lesions. Data presented today
suggest that TYSABRI significantly increased the proportion of
disease-free patients by 79% over two years compared with placebo (28%
vs. 6%, respectively; p<0.001).

Cost Effectiveness of MS Therapies

A model was constructed by Xcenda, formerly Applied Health
Outcomes, to compare the cost per relapse avoided among the five
approved disease-modifying MS therapies to treat relapsing forms of
MS. Overall cost of therapy was calculated using the US wholesale
acquisition drug cost, and costs associated with drug administration,
patient monitoring and treatment of relapses. The costs associated
with adverse events were not assessed as part of this model.
Effectiveness was defined as the number of relapses avoided with
treatment, which was calculated as the number of relapses for a
non-treated population multiplied by published relapse rate reductions
for the therapies.(1) Based on the model developed, the cost per
relapse per year avoided was lowest for TYSABRI. The cost per relapse
avoided for TYSABRI was between $12,730 and $23,274 lower than that of
the other approved disease-modifying therapies.

Data Show TYSABRI Had Improvement in Quality of Life Assessments

Quality of Life (QoL) was assessed using three different measures,
the Multiple Sclerosis Quality of Life Inventory (MSQLI), the Short
Form-36 Health Survey (SF-36), which is a component of the MSQLI, and
a Visual Analogue Scale (VAS). The MSQLI is an MS-specific battery of
10 scales that measure disease impact on QoL, including fatigue, pain,
sexual function, bowel and bladder function, visual impairment, mental
health and need for social support. The SF-36 is comprised of 36
questions designed to assess patients' physical and mental well-being.
General well-being was also measured using the VAS.

In data presented today from the AFFIRM study, patients in the
TYSABRI-treated group realized a significant improvement in physical
measures of the SF-36 compared with a decline in the placebo-treated
group (p=0.003). A significant improvement was also seen in the mental
component of the SF-36 in patients treated with TYSABRI compared with
a decline in the placebo-group (p=0.011). Significant benefits were
also seen using the VAS (p=0.007).

About TYSABRI

In the US, TYSABRI is approved as a monotherapy treatment for
relapsing forms of MS. TYSABRI increases the risk of progressive
multifocal leukoencephalopathy (PML), an opportunistic viral infection
of the brain that usually leads to death or severe disability.
Patients should be monitored at regular intervals for any new or
worsening signs or symptoms suggestive of PML. Because of the
increased risk of PML, TYSABRI is generally recommended for patients
who have had an inadequate response to, or are unable to tolerate,
alternate MS therapies. It is available in the US only through a
restricted distribution program called the TOUCH Prescribing Program.
According to product labeling, after two years, TYSABRI treatment led
to a 67% relative reduction (p<0.001) in the annualized relapse rate
compared to placebo and reduced the relative risk of disability
progression by 42% (p<0.001). TYSABRI treatment also resulted in
sustained and statistically significant reductions in brain lesion
activity as measured by MRI. Changes in MRI findings often do not
correlate with changes in the clinical status of patients (e.g.,
disability progression). The prognostic significance of the MRI
findings in these studies has not been evaluated.

In the European Union, TYSABRI is indicated as a single
disease-modifying therapy in highly active relapsing-remitting MS
patients. Because of the increased risk of PML, it is for patients
with high disease activity despite treatment with a beta-interferon or
in patients with rapidly evolving severe relapsing-remitting MS.
According to product labeling in the EU, 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).

Serious adverse events that occurred in TYSABRI-treated patients
included hypersensitivity reactions (e.g., anaphylaxis), infections,
depression and gallstones. 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. Herpes infections were slightly more common in patients
treated with TYSABRI. Serious opportunistic and other atypical
infections have been observed in TYSABRI-treated patients, some of
whom were receiving concurrent immunosuppressants. 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.

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 oncology, neurology
and immunology. As a global leader in the development, manufacturing,
and commercialization of novel therapies, Biogen Idec transforms
scientific discoveries into advances in human healthcare. 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.

(1) The relapse reduction rates used were: TYSABRI was 67%, AVONEX
(Interferon beta-1a IM) 32%, Betaseron(R) (Interferon beta-1b) 34%,
Copaxone(R) (glatiramer acetate) 29%, and Rebif(R) (Interferon beta-1a
SC) 32%.