In a paper released on Monday, Martin S. Eichenbaum and Sergio Rebelo of Northwestern University, with Mathias Trabandt of the Free University in Berlin, used the E.P.A.’s number to figure the optimal way to slow the spread of the disease without economic costs that exceed the benefits.

The economy would contract sharply even without a government-imposed lockdown as people chose to stay away from workplaces and stores, hoping to prevent contagion. In that case of voluntary isolation, Mr. Eichenbaum and his colleagues estimated that U.S. consumer demand would decline by $800 billion in 2020, or about 5.5 percent.

Based on epidemiological projections, as the virus ran unchecked, it would quickly expand to infect somewhat over half the population before herd immunity would slow its course. Assuming a death rate of about 1 percent of those infected, about 1.7 million Americans would die within a year.

A policy to contain the virus by reducing economic activity would slow the progression of the virus and reduce the death rate, but it would also impose a greater economic cost.

Mr. Eichenbaum and his colleagues say the “optimal” policy — assessing economic losses alongside lives — requires restrictions that slow the economy substantially. Under their approach, the decline in consumption in 2020 more than doubles, to $1.8 trillion, but the deaths drop by half a million people. That would amount to $2 million in lost economic activity per life saved.

In this instance, “you want to make the recession worse,” Mr. Eichenbaum said. But an important corollary is that there are limits to the sacrifice: Beyond a certain point, it would not be worth it to lose more economic activity in order to save more people.

The model, he noted, is heavily dependent on the assumptions that go into it, meant to convey the magnitude of the trade-offs. And the economists are still tweaking. The cost-benefit ratio will change if one considers that the health system might become overwhelmed by Covid-19 cases, increasing mortality rates. That would justify a more aggressive lockdown that ramped up more quickly.