TYSABRI increases the risk of progressive multifocal leukoencephalopathy (PML), an opportunistic viral infection of the brain, which usually leads to death or severe disability. Infection by the JC virus (JCV) is required for the development of PML and patients who are anti-JCV antibody positive have a higher risk of developing PML. Factors that increase the risk of PML are presence of anti-JCV antibodies, prior immunosuppressant use, and longer TYSABRI treatment duration. Patients who have all three risk factors have the highest risk of developing PML. Other serious adverse events that have occurred in TYSABRI-treated patients include hypersensitivity reactions (e.g., anaphylaxis) and infections, including opportunistic and other atypical infections. Clinically significant liver injury has also been reported in the post-marketing setting. A list of adverse events can be found in the full TYSABRI product labeling for each country where it is approved.TYSABRI is marketed and distributed by Biogen Idec Inc. and Elan Corporation, plc. For full prescribing information, including boxed warning and important safety information, and more information about TYSABRI, please visit www.biogenidec.com or www.elan.com. Safe Harbor This press release contains forward-looking statements, including statements about potential product launches, 2012 financial guidance, clinical trial readouts and regulatory submissions. These forward-looking statements may be accompanied by such words as “anticipate,” “believe,” “could,” “estimate,” “expect,” “forecast,” “intend,” “may,” “plan,” “project,” “target,” “will” and other words and terms of similar meaning. You should not place undue reliance on these statements. These statements involve risks and uncertainties that could cause actual results to differ materially from those reflected in such statements, including our dependence on our three principal products, AVONEX, TYSABRI and RITUXAN, the importance of TYSABRI’s sales growth, uncertainty of success in commercializing other products, product competition, the occurrence of adverse safety events with our products, changes in the availability of reimbursement for our products, adverse market and economic conditions, our dependence on collaborations and other third parties over which we may not always have full control, problems with our manufacturing processes and our reliance on third parties, failure to comply with government regulation, our ability to protect our intellectual property rights and have sufficient rights to market our products together with the cost of doing so, the risks of doing business internationally, failure to execute our growth initiatives, charges and other costs relating to our properties, fluctuations in our effective tax rate, our ability to attract and retain qualified personnel, product liability claims, fluctuations in our operating results, the market, interest and credit risks associated with our portfolio of marketable securities, environmental risks, change of control provisions in our collaborations and the other risks and uncertainties that are described in the Risk Factors section of our most recent annual or quarterly report and in other reports we have filed with the SEC.