  We present a simple technique to compare the development of the Covid-19
epidemic in different regions, based only on the time series of confirmed
cases. Weekly new infections, taken for every day, are interpreted as infection
potential of Covid-19. We derive a robust time-varying reproduction rate for
the infection potential, including asymptomatic cases, which does not depend on
death rate or testing intensity. It requires few assumptions and shows a more
plausible time course than official reproduction rates in several countries.
