“The best case is that the virus mutates and actually dies out,” said Dr. Larry Brilliant, an epidemiologist who as a young doctor was part of the fight to eradicate smallpox. Brilliant was a consultant for the movie “Contagion,” in which a virus evolved to become more deadly, but that’s the exception. “Only in movies do viruses seem to become worse,” he explained.

Two other lethal coronaviruses, SARS and MERS, both petered out, and that is possible here. “My hope is that Covid-19 will not survive,” said Dr. Charles G. Prober, a professor at Stanford Medical School.

Several countries have shown that decisive action can turn the tide on Covid-19, at least for a time. China, astonishingly, on Thursday reported not a single new case of domestic transmission. While China is still vulnerable to a second wave, it has apparently shown that the virus can be squelched.

The West isn’t going to copy the coercive tactics of China, but Singapore, Taiwan, South Korea and Hong Kong have also demonstrated that, at least temporarily, the virus can be controlled.