Withering

From the White Wolf Wiki, the most complete White Wolf reference

Withering is a general loss of potency in the vitae affecting vampires during Gehenna (event). It affects first the elders, then progressing to the higher generations.

The Kindred begin losing their capacity to use their blood as they would normally do. They activate some discipline, for example, and the blood is spent, but no effect happens. The initial symptoms might be experienced as an unusual potency in all the disciplines. Soon, though, they become unable to use most of their powers, or even regenerate any damage received.

The only remedy seems to be diablerizing other vampires.