There remains deep uncertainty about the new coronavirus' mortality rate, with the high-end estimate that it is up to 20 times that of the flu, but some estimates go as low as 0.16 percent for those affected outside of China’s overwhelmed Hubei province. About on par with the flu.

Wasn’t there something strange, the student asked, about the extreme disparity in public reactions?

Ann Bostrom, the dinner’s public policy co-host, laughed when she recounted the evening. The student was right about the viruses, but not about people, said Dr. Bostrom, who is an expert on the psychology of how humans evaluate risk.

While the metrics of public health might put the flu alongside or even ahead of the new coronavirus for sheer deadliness, she said, the mind has its own ways of measuring danger. And the new coronavirus disease, named COVID-19 hits nearly every cognitive trigger we have.

That explains the global wave of anxiety.

Of course, it is far from irrational to feel some fear about the coronavirus outbreak tearing through China and beyond.

But there is a lesson, psychologists and public health experts say, in the near-terror that the virus induces, even as serious threats like the flu receive little more than a shrug. It illustrates the unconscious biases in how human beings think about risk, as well as the impulses that often guide our responses — sometimes with serious consequences.