  Modified gravity models which include an additional propagating degree of
freedom are typically studied in the quasi-static limit, where the propagation
is neglected, and the wave equation of the field is replaced with a
Poisson-type equation. Recently, it has been proposed that, in the context of
models with symmetron- or chameleon-type screening, scalar waves from
astrophysical or cosmological events could have a significant effect on the
screening of the Solar System, and hence invalidate these models. Here, we
quantitatively investigate the impact of scalar waves by solving the full field
equation linearised in the wave amplitude. In the symmetron case, we find that
the quantitative effect of waves is generally negligible, even for the largest
amplitudes of waves that are physically expected. In order to spoil the
screening in the Solar System, a significant amount of wave energy would have
to be focused on the Solar System by arranging the sources in a spherical shell
centred on Earth. In the chameleon case, we are able to rule out any
significant effects of propagating waves on Solar System tests.
