Towards the possibility of a self-maintained vacuum-traversable wormhole

We calculate the renormalised vacuum expectation values of the electromagnetic stress-energy tensor in the static spherically-symmetrical wormhole topology. Let us suppose that the derivatives of the metric tensor over a radial distance are sufficiently small (on the scale of the radius) to ensure the validity of a quasiclassical (WKB) expansion over the derivatives. Then we find that violation of the averaged weak energy condition takes place irrespective of the detailed form of the metric. This is a necessary condition for the electromagnetic vacuum to be able to support the wormhole geometry.