Holding a QR code up to a scanner is second nature to many people these days. From digital boarding passes to proof of purchase, they have become ubiquitous in an increasingly paperless world. So it requires no great leap of the imagination to picture British people beeping themselves into stadiums and pubs with a little black and white square that proves they have been vaccinated against Covid. Are they not the obvious solution to get the country's hospitality and entertainment industries open again? The reality is far more complex and, for every question that vaccine passports (or certificates, as the Government prefers) appear to answer, they pose many more. Yet, as the Government knows all too well, it's not an issue that can just be left for the market to decide. Perhaps the first question facing vaccine certificates is when exactly to introduce them. The first option would be to do so as soon as possible, but this would create a scenario in which only a select slice of society would have access to reopened services. "If we were going to introduce this tomorrow, which isn't the plan, you'd exclude everyone 65 and under," says Melinda Mills, a professor of demography at Oxford University and a lead author of a Royal Society report on the criteria vaccine passports would need to meet.