  Lockdown procedures have been proven successful in mitigating the spread of
the viruses in this COVID-19 pandemic, but they also have devastating impact on
the economy. We use a modified Susceptible-Infectious-Recovered-Deceased model
with time dependent infection rate to simulate how the infection is spread
under lockdown. The economic cost due to the loss of workforce and incurred
medical expenses is evaluated with a simple model. We find the best strategy,
meaning the smallest economic cost for the entire course of the pandemic, is to
keep the strict lockdown as long as possible.
