  We generalize our virial approach to study the neutral current neutrino
response of nuclear matter at low densities. In the long-wavelength limit, the
virial expansion makes model-independent predictions for neutrino-nucleon
scattering rates and the density S_V and spin S_A responses. We find S_A is
significantly reduced from one even at low densities. We provide a simple fit
S_A^f(n,T,Y_p) of the axial response as a function of density n, temperature T
and proton fraction Y_p. This fit reproduces our model independent virial
results at low densities and reproduces the Burrows and Sawyer random phase
approximation (RPA) results at high densities. Our fit can be incorporated into
supernova simulations in a straight forward manner. Preliminary one dimensional
supernova simulations suggest that the reduction in the axial response may
enhance neutrino heating rates in the gain region during the accretion phase of
a core-collapse supernovae.
