In 40 percent of markets around the country, hospitals would not be able to make enough room for all the patients who became ill with Covid-19, even if they could empty their beds of other patients. That statistic assumes that 40 percent of adults become infected with the virus over 12 months, a scenario described as “moderate” by the team behind the calculations.

These numbers are not exact predictions. In many ways, they reflect a worst-case scenario, since they do not take into account the efforts hospitals can make to quickly increase capacity during an emergency. Around the country, hospitals have begun canceling elective operations and speeding home patients with less critical ailments. Those efforts could increase the number of free beds available for coronavirus patients. In a half-dozen interviews, hospital executives estimated that they could increase their capacity between 20 percent and 70 percent.

Yet the Harvard estimates suggest that the coronavirus outbreak could require significantly more resources than that. In hard-hit Italy, hospitals have been rationing care for older patients who are severely ill with the virus.