JOURNAL OF MATHEMATICAL PHYSICS, vol.34, no.2, pp.690-699, 1993 (Journal Indexed in SCI)
It is shown that quantum fluctuations, in particular vacuum polarization, vanish in the background of a spherical impulsive wave solution of the Einstein field equations, recently found by Nutku and Penrose. The calculation is done in first-order perturbation theory but arguments are given why it should persist to all orders.