  Using dispersion relations, we derive the complete virtual QED contributions
to Bhabha scattering due to vacuum polarization effects in photon propagation.
We apply our result to hadronic corrections and to heavy lepton and top quark
loop insertions. We give the first complete estimate of their net numerical
effects for both small and large angle scattering at typical beam energies of
meson factories, LEP, and the ILC. The effects turn out to be smaller, in most
cases, than those corresponding to electron loop insertions, but stay, with
amounts of typically one per mille, of relevance for precision experiments.
Hadronic corrections themselves are typically about 2-3 times larger than those
of intermediate muon pairs (the largest heavy leptonic terms).
