  We use effective field theory and thermal field theory to study the dynamical
screening effect in the QED plasma on the $\alpha$-$\alpha$ scattering at the
$^8$Be resonance. Dynamical screening leads to an imaginary part of the
potential which results in a thermal width for the resonance and dominates over
the previously considered static screening effect. As a result, both the
resonance energy and width increase with the plasma temperature. Furthermore,
dynamical screening can have a huge impact on the $\alpha$-$\alpha$ thermal
nuclear scattering rate. For example, when the temperature is around $10$ keV,
the rate is suppressed by a factor of about $900$. We expect similar thermal
suppressions of nuclear reaction rates to occur in those reactions dominated by
an above threshold resonance with a thermal energy. Dynamical screening effects
on nuclear reactions can be relevant to cosmology and astrophysics.
