So far, everything I've read says:

"Shares of Biogen fell $12.26, or 17.6 percent, to $57.49 in after-hours trading."

"Shares of Elan fell $7.60, or 37.9 percent, to $12.45."

Something to be concerned about though, which is a new consideration for users:

"The three 2005 cases (of PML) involved patients who were simultaneously taking another MS-fighting drug; such combined therapy has been banned since 2005.

The patients in the most recent case had a history of taking other MS drugs but had been on Tysabri alone for at least 14 months, according to the SEC filing."

(From what I've read, one patient was on Tysabri for 17 months, and the other for 14 months.)

http://biz.yahoo.com/ap/080731/bioge...drug.html?.v=3

Even though Biogen has been forthright about the potential for new cases of PML to occur (no one can sue ), there was always the thought that the first cases occurred because the people had used Avonex as a combination therapy and/or the patient (Crohn's) had been on very strong immunosuppressants previously. So far, it doesn't sound like these two people were using anything else (except maybe steroids, which have not been considered a problem with Tysabri).

Biogen Idec and Elan Corporation, plc Host Conference Call For Investment Community, Scheduled to start Fri, Aug 1, 2008, 8:30 am Eastern:

http://biz.yahoo.com/cc/9/96099.html

Cherie