Complex sentence: A phase 2 study of a CMV vaccine published in 2009 indicated an efficacy of 50%, thus the protection provided was limited and a number of subjects contracted CMV infection despite the vaccination.
Split into simpler sentences: A phase 2 study of a CMV vaccine published in 2009 indicated an efficacy of 50%, with limited durability. Thus the protection provided was limited and a number of subjects contracted CMV infection despite the vaccination.