  Zhang et al. (2020) used linear regression to quantify the effect of
lockdowns on the number of cases of COVID-19. We show using differential
equations from the susceptible-exposed-infected-recovered (SEIR) model and with
an example from another location not previously considered that the Zhang et
al. analysis should not be considered sound evidence that mask mandates are
sufficient to control or the primary factor controlling the spread of COVID-19.
