Some of the projections for covid-19 spread in the U.S. have been grave. A forecast produced last month by University of Nebraska Medical Center professor James Lawler on behalf of the American Hospital Association, for example, put the potential death toll in the hundreds of thousands if efforts to mitigate the epidemic failed.

Another forecast, developed by former Centers for Disease Control and Prevention director Tom Frieden at the nonprofit organization Resolve to Save Lives, found that deaths in the U.S. could range widely, depending on what percentage of the population gets infected and how lethal the disease proves to be. Frieden, who oversaw the 2009 H1N1 influenza pandemic, the 2014 Ebola epidemic and the 2016 Zika epidemic, says in a worst-case scenario, but one that is not implausible, half the U.S. population would get infected and more than one million people would die.

His team put together a simple table that looks at various scenarios using case fatality ratios ranging from .1, similar to seasonal flu, to .5, a moderately severe pandemic, and 1.0, a severe one. The infection rate ranged from 0.1 percent of the population to 50 percent. That put the range of deaths from 327 (best case) to 1,635,000 (worst case). The deaths would not necessarily happen over a month or a year, but could happen in two or three years, he said.