Alongside my main job, for a few hours a year I’m an Associate Lecturer in Public Health at Northumbria University. My biggest single contribution in this role is a full day seminar on health protection, which forms part of the Master of Public Health course. By sheer coincidence, this year’s seminar fell on 15 March—today—and so I “treated” the students to a brief lecture version of this blog post from a couple of years ago. They seemed to like it!