Definition of "fiercest"

America’s poverty line is $63 a day for a family of four. In the richer parts of the emerging world $4 a day is the poverty barrier. But poverty’s scourge is fiercest below $1.25 ([…]): people below that level live lives that are poor, nasty, brutish and short.

2013 June 1, “Towards the end of poverty”, in The Economist‎, volume 407, number 8838, page 11