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This week marks a strange anniversary—it’s five years since most of us first heard about a virus causing a mysterious “pneumonia.” A virus that we later learned could cause a disease called covid-19. A virus that swept the globe and has since been reported to have been responsible for over 7 million deaths—and counting.

I first covered the virus in an article published on January 7, 2020, which had the headline “Doctors scramble to identify mysterious illness emerging in China.” For that article, and many others that followed it, I spoke to people who were experts on viruses, infectious disease, and epidemiology. Frequently, their answers to my questions about the virus, how it might spread, and the risks of a pandemic were the same: “We don’t know.”

We are facing the same uncertainty now with H5N1, the virus commonly known as bird flu. This virus has been decimating bird populations for years, and now a variant is rapidly spreading among dairy cattle in the US. We know it can cause severe disease in animals, and we know it can pass from animals to people who are in close contact with them. As of this Monday this week, we also know that it can cause severe disease in people—a 65-year-old man in Louisiana became the first person in the US to die from an H5N1 infection.

Scientists are increasingly concerned about a potential bird flu pandemic. The question is, given all the enduring uncertainty around the virus, what should we be doing now to prepare for the possibility? Can stockpiled vaccines save us? And, importantly, have we learned any lessons from a ...