Another promising sign comes from those who contracted the original SARS coronavirus in 2003. The T cells of people who were infected at the time reliably recognized the spike protein from the virus in lab experiments 17 years later. Gandhi believes that this memory, while not always as protective as having high levels of neutralizing antibodies in your blood, will likely be sufficient to prevent severe disease. “Do I think that we’ll have lifelong immunity from severe infection?” she said. “I am very heartened that we will.”

If that’s the case, then COVID-21 will eventually be a milder, less deadly version of the illness that we started with last year. “The worst-case scenario is we render it a cold,” Gandhi said. “The best-case is we reach herd immunity and the virus goes almost entirely away.”

But others expect a much worse worst-case scenario, in which immunity to severe disease is only temporary. The biologist and former Harvard professor William Haseltine warns against the rosy view: “It seems to me clear that the T-cell theory isn’t going to hold up,” he told me. Although our memory cells could continue to recognize the virus, that won’t necessarily be enough to give us meaningful protection. The disease might end up being milder the second time around, or after vaccination, but he worries that, as the virus mutates, it also could get worse. As for herd immunity, Haseltine called that a “fantasy.” “The best we’ll get is seasonal herd immunity. We have 60 years of experience with coronaviruses, and they come back every year.”