  This paper investigates semiclassical backreaction of a conformally coupled
massless scalar field on the geometrical background of a nearly spinning cosmic
string - the spin density is smaller than, but arbitrarily close to, the
dislocation parameter. As the spin density approaches the dislocation
parameter, it is shown that an "ergoregion" spreads indefinitely around the
cosmic string, boosting along the string axis the once static observers.
Considering that the geometrical background contains closed timelike curves
when the spin density exceeds the dislocation parameter, it is argued that the
appearance of the "ergoregion" may be part of a chronology protection mechanism
that takes place in related non stationary geometries.
