BSO reports on their website:
BSO Music Director James Levine has had to withdraw from his remaining scheduled concerts of the BSO's 2010-11 season, March 3-19, including Symphony Hall, Carnegie Hall, New Jersey Performing Arts Center, and Kennedy Center appearances, though all concerts will take place as scheduled.
Maestro Levine is forced to cancel appearances due to ill effects from a recent procedure addressing his ongoing back issues, further complicated by a viral infection.
Updated program information will be released at some point on Wednesday, March 2.
We wish the Maestro all our best.