( BW)(MA-BIOGEN/ELAN)(BIIB)(ELN) CHMP Issues Positive Opinion for
TYSABRI(R) as a Treatment for Relapsing-Remitting Multiple Sclerosis

    Business Editors/Health/Medical Writers

    CAMBRIDGE, Mass. and DUBLIN, Ireland--(BUSINESS WIRE)--April 28,
2006--Biogen Idec (NASDAQ: BIIB) and Elan Corporation, plc (NYSE: ELN)
announced today that the Committee for Medicinal Products for Human
Use (CHMP), the scientific committee of the European Medicines Agency
(EMEA), issued a positive opinion recommending marketing authorization
for TYSABRI(R) (natalizumab) as a treatment for relapsing-remitting
multiple sclerosis (MS) to delay the progression of disability and
reduce the frequency of relapses. The Committee recommended that
TYSABRI be used as single disease modifying therapy either in patients
with highly active relapsing-remitting MS who have failed to respond
to treatment with a beta-interferon, or in patients who have rapidly
evolving severe relapsing-remitting MS.
    In making its recommendation, the CHMP reviewed available data
from the development of TYSABRI, including data from the Phase III
AFFIRM monotherapy trial, the Phase III SENTINEL trial in which
TYSABRI was added to AVONEX(R) (Interferon beta-1a); and a
comprehensive safety analysis, which included the assessments for
cases of progressive multifocal leukoencephalopathy (PML). The CHMP
also reviewed a Risk Management plan to assess and minimize risks,
including PML and other serious opportunistic infections.
    The CHMP's positive recommendation for TYSABRI will be considered
for final marketing approval by the European Commission. Final
approval customarily follows the CHMP's recommendation, which the
companies anticipate will be this summer. The European Commission is
the final decision-making body for all centrally-reviewed medicinal
products that are to be introduced in the EU market.

    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
the potential therapeutic uses and regulatory path forward of TYSABRI.
The commercial potential and regulatory path forward of TYSABRI are
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 unable to adequately address
concerns or questions raised by FDA or European regulatory authorities
during the regulatory review process, that concerns may arise from
additional data or analysis, or that the companies may encounter other
unexpected delays or hurdles. There is also no assurance that the
companies will be able to resume marketing and sales of TYSABRI. 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 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.

    --30--NC/bo*

    CONTACT: Media Contacts:
             Biogen Idec                     
             Amy Brockelman, 617-914-6524                
             or
             Katja Buller, 41 41 392 1792             
             or
             Elan                     
             Davia B. Temin, 212-407-5740         
             or
             Elizabeth Headon, 353-1-498-0300           
             or                       
             Investor Contacts:
             Biogen Idec                     
             Oscar Velastegui, 617-679-2812                
             or
             Elan                           
             Emer Reynolds, 353 1 709 4000
             or
             Chris Burns, 800-252-3526