To determine the impact of early interventions, we used growth rates in cumulative deaths calculated by the Institute for Health Metrics and Evaluation at the University of Washington from the date that social distancing measures were introduced until the predicted end of the epidemic, and applied them to case numbers from earlier points when such measures could hypothetically have been put into effect.

The absolute numbers are largely beside the point. No model is a crystal ball, and there is far too much uncertainty in the trajectory of the U.S. epidemic to conclude that a certain prediction will be borne out. What matters more is the relative effect of moving earlier rather than later in trying to contain the spread. The relative effects of moving earlier necessarily depend on the assumed rate of growth, but the general conclusion is the same: Earlier is better.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, said as much on Sunday on the CNN program “State of the Union.”

“Obviously, you could logically say that if you had a process that was ongoing and you started mitigation earlier, you could have saved lives,” he said. But, he noted, “there was a lot of pushback about shutting things” early in the outbreak.

Whatever the final death toll is in the United States, the cost of waiting will be enormous, a tragic consequence of the exponential spread of the virus early in the epidemic.