  The renormalised vacuum expectation values of massless fermion
(conventionally call it neutrino) stress-energy tensor are calculated in the
static spherically-symmetrical wormhole topology. Consider the case when the
derivatives of metric tensor over radial distance are sufficiently small (in
the scale of radius) to justify studying a few first orders of quasiclassical
(WKB) expansion over derivatives. Then we find that violation of the averaged
weak energy condition takes place irrespectively of the detailed form of
metric. This is a necessary condition for the neutrino vacuum to be able to
support the wormhole geometry. In this respect, neutrino vacuum behaves like
electromagnetic one and differs from the conformal scalar vacuum which does not
seem to violate energy conditions for slowly varied metric automatically, but
requires self-consistent wormhole solution for this.
