Regarding non-standard monetary policy measures, we confirm that the monthly asset purchases of € billion are intended to run until the end of March 2017, or beyond, if necessary, and in any case until the Governing Council sees a sustained adjustment in the path of inflation consistent with its inflation aim.
“The Optimal Inflation Rate in New Keynesian Models: Should  Central Banks Raise Their Inflation Targets in Light of the Zero Lower Bound?”, The Review of Economic Studies, Volume 79, Issue 4, 1 October 2012, pp. 1371–1406.