Dean Michelle Williams; Ben Gebo / Harvard Chan School Public health, I’ve often said, is everywhere and nowhere. Most of us take the cleanliness of our air and water for granted until there’s a contamination scare. We don’t give food supply chains a second thought unless there’s a shortage of milk or flour. And, until recently, we’d hop on a train or bus without worrying about what airborne viruses might be along for the ride. In other words, the impact of public health is largely invisible—until there’s a crisis. Only then do we become acutely aware of the role it plays in our daily lives.