B757 pilot reported the right engine developed a vibration during cruise; resulting diversion to a suitable airport.

Narrative

I came up from my rest to find the Captain on the satcom with Dispatch and Maintenance Control discussing an engine vibration caution event. The First Officer told me that during cruise the right engine vibrations went into the yellow band and remained there until the thrust was reduced. After the QRC did not repair the issue; and discussion with Maintenance Control; Dispatch; and ourselves; we elected to request priority handling with ZZZ and divert back to ZZZ. We continued the diversion with the R Engine thrust lever reduced to keep the vibrations in the normal band. We informed ZZZ Center that we'd like crash/fire/rescue standing by on landing. A normal landing and taxi to the gate was performed. Additionally on our diversion; a medical event occurred in the cabin. A passenger fainted and fell leaving the door 2 lavatory. The flight attendants (FAs) gathered a nurse and a doctor to assist. Doctor advised to continue to ZZZ as no immediate rush was necessary. The passenger recovered and was monitored for the remainder of the flight with no further health issues.