I had my flu jab last week and have no idea how my immune system responded. So I was intrigued to hear about a new test that is being developed to measure immune health. Writer David Ewing Duncan hoped that the test would reveal more about his health than any other he’d ever taken. The test David took was developed by John Tsang at Yale University and his colleagues. The team wanted to work out a way of measuring how healthy a person’s immune system might be.