Because the baby boomers have not yet started to retire in force and accordingly the ratio of retirees to workers is still relatively low, we are in the midst of a demographic lull.
For a focus on developments within the Great Recession, see David M. Cutler, Ellen Meara, and Seth Richards-Shubik (2012), “Unemployment and Disability: Evidence from the Great Recession”, NBER Retirement Research Center Paper Series NB 12–12 (Cambridge, Mass. : National Bureau of Economic Research, September).