(NYTIMES) - As an intensive care unit doctor, I often find myself thinking about the apparent randomness of infectious disease. Two people go out to dinner and have the same meal; one ends up in the emergency room with food poisoning, but the other does not. The seasonal flu runs through an entire family, except for one individual who remains healthy.

Doctors look for the vulnerabilities that we can see to explain these outcomes, like age, vaccination status and underlying conditions, but we are often left without answers. The unpredictability of the coronavirus has made clear just how much we don't know.