The Tanglewood Festival has announced a cast change for its August 12 and 13 concerts.

The company said, “With great regret, after testing positive for COVID-19, cellist Yo-Yo Ma must withdraw from this week’s scheduled Tanglewood appearances, including today’s now canceled (8/10) Open Cello Workshop, Saturday’s (8/12) Open Rehearsal, and Sunday’s (8/13) Boston Symphony concert.”

As a result, “Unparalleled American soprano Renée Fleming has graciously agreed to step in to join the BSO on Saturday morning and Sunday afternoon, performing songs by Richard Strauss in place of the Shostakovich Cello Concerto No. 1 that was originally scheduled.”

Fleming will join Andris Nelsons in a program that will also include music by Stravinsky and Julia Adolphe.