  A model of the spread of viruses in selected city and in a network of cities
is considered, taking into account the delay caused by the long incubation
period of the virus. The effect of delay effects is shown in comparison with
pandemics without such delay. A temporary asymmetry of the spread of infection
has been identified, which means that the time for a pandemic to develop
significantly exceeds the time for its completion. Model calculations of the
spread of viruses in a network of interconnected large and small cities were
carried out, and dynamics features were revealed in comparison with the spread
of viruses in a single city, including the possibility of reinfection of
megalopolis.
