Lipsitch predicts that, within the coming year, some 40 to 70 percent of people around the world will be infected with the virus that causes COVID-19. But, he clarifies emphatically, this does not mean that all will have severe illnesses. “It’s likely that many will have mild disease, or may be asymptomatic,” he said. As with influenza, which is often life-threatening to people with chronic health conditions and of older age, most cases pass without medical care. (Overall, around 14 percent of people with influenza have no symptoms.)

Lipsitch is far from alone in his belief that this virus will continue to spread widely. The emerging consensus among epidemiologists is that the most likely outcome of this outbreak is a new seasonal disease—a fifth “endemic” coronavirus. With the other four, people are not known to develop long-lasting immunity. If this one follows suit, and if the disease continues to be as severe as it is now, “cold and flu season” could become “cold and flu and COVID-19 season.”

At this point, it is not even known how many people are infected. As of Sunday, there have been 35 confirmed cases in the U.S., according to the World Health Organization. But Lipsitch’s “very, very rough” estimate when we spoke a week ago (banking on “multiple assumptions piled on top of each other,” he said) was that 100 or 200 people in the U.S. were infected. That’s all it would take to seed the disease widely. The rate of spread would depend on how contagious the disease is in milder cases. On Friday, Chinese scientists reported in the medical journal JAMA an apparent case of asymptomatic spread of the virus, from a patient with a normal chest CT scan. The researchers concluded with stolid understatement that if this finding is not a bizarre abnormality, “the prevention of COVID-19 infection would prove challenging.”