  We show how the standard field theoretical language based on creation and
annihilation operators may be used for a straightforward derivation of an
SIR-type stochastic model for COVID-19 epidemic, from which we obtain the time
evolution of the mean number of infectious (active cases) and deceased
individuals. In order to capture the effects of lockdown and social distancing,
we use a time-dependent infection rate. The results are in good agreement with
the data for three different waves of epidemic activity in South Korea.
