Economic irreversibility in pandemic control processes: Rigorous modeling of delayed countermeasures and consequential cost increases

After the first lockdown in response to the COVID-19 outbreak, many countries faced difficulties in balancing infection control with economics. Owing to limited prior knowledge, economists began researching this issue and found that infection control processes significantly affect economic efficiency. A study using economic parameters in the United Kingdom numerically demonstrated that keeping the infected population stationary is economically optimum. However, a universally applicable solution, indispensable for the guiding principles of infection control, has not yet been developed because of the methodological limitations of simulation studies. Here, I prove the universal result of economic irreversibility by applying the idea of thermodynamics to pandemic control. This means that once the infected population increases, society cannot return to its previous state without incurring extra expenditure. This universal result is analytically obtained by focusing on the infection-spreading phase of pandemics and applies to COVID-19 and other infectious diseases, regardless of herd immunity. The findings suggest that economic irreversibility is a guiding principle for balancing infection control with economic effects.