  We show that 1-loop quantum corrections to the potential energy density in
supersymmetric hybrid inflation, outside the inflationary valley, can not be
neglected. A method is presented to calculate these 1-loop corrections and they
are applied to the case of D-term hybrid inflation, where a significant amount
of inflation is shown to occur after spontaneous symmetry breaking. Taking this
into account improves the agreement with WMAP measurements. A gauge coupling of
up to 0.3 is still consistent with the CMB density perturbation. The spectral
index is predicted in between 0.98 and 1.00 and the cosmic string contribution
to the CMB anisotropy is sufficiently reduced.
