  We apply a formalism accounting for thermal effects (such as modified
Sommerfeld effect; Salpeter correction; decohering scatterings; dissociation of
bound states), to one of the simplest WIMP-like dark matter models, associated
with an "inert" Higgs doublet. A broad temperature range T ~ M/20...M/10^4 is
considered, stressing the importance and less-understood nature of late
annihilation stages. Even though only weak interactions play a role, we find
that resummed real and virtual corrections increase the tree-level overclosure
bound by 1...18%, depending on quartic couplings and mass splittings.
