  Since November 6$^{\mathrm{th}}$, 2020, Italian regions have been classified
according to four levels, corresponding to specific risk scenarios, for which
specific restrictive measures have been foreseen. By analyzing the time
evolution of the reproduction number $R_t$, we estimate how much different
restrictive measures affect $R_t$, and we quantify the combined effect of the
diffusion of virus variants and the beginning of the vaccination campaign upon
the $R_t$ trend. We also compute the time delay between implementation of
restrictive measures and the resulting effects. Three different models to
describe the effects of restrictive measures are discussed and the results are
cross-checked with two different algorithms for the computation of $R_t$.
