The economic justification for any public policies to mitigate the Covid-19 pandemic
hinge on the presence of externalities. The mere fact that Covid-19 is deadly would not justify a public policy response if all of the risks associated with contracting the disease were completely internalized to individuals making decisions. Individuals weighing their own marginal benefits of engaging in activities involving a risk of catching the disease against the probability of catching the disease times the value of their expected health outcome would lead to the socially optimal amount of disease and death. As with any risky activity that also has benefits, that number would exceed zero. Unfortunately, when individuals contract Covid-19 they also contract the possibility of infecting others with the disease. If individuals do not account for how their own activities risk their contracting the disease, this raises the risk of contraction for others, causing a transmission externality. It is a classic situation where private marginal costs diverge from the full social marginal costs, so that individuals left to their own devices would engage in inefficiently too much risk taking, leading to inefficiently too much disease spread and death.
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