Date	Event	Description
23 May 2013	New citation required but conclusions have not changed	The additional evidence did not change the conclusions of this review.
20 February 2013	New search has been performed	Added six new studies: Eriksson 2008, Freeman 2010, Glaxo 1996, Glaxo 1996a, Glaxo 2001, Steiner 2008. Some studies were split into multiple comparisons in earlier versions of the review, each with a separate study reference; such studies have been combined and referenced as a single study in this update. Excluded three previously included studies: Sundblad 1992, Sundblad 1993, Veeninga 1990.