Like countless others, I was convinced I’d already had coronavirus. I travelled a lot at the start of the year: a hellish, delayed, 30-hour flight to the UK from Australia, where I had spent Christmas and New Year, a skiing trip with friends in the Swiss Alps, and a week at the World Economic Forum in Davos, where I shook hundreds of hands in stuffy conference rooms by day and at crammed cocktail parties by night.

In February, I developed the worst chest infection of my life, so persistent that one night, while eating in a restaurant, I had to go home mid-meal because I could not stop coughing. I discounted any evidence that contradicted my hypothesis: at no point had I developed a noticeable fever, my sense of taste and smell had remained intact, and I did not seem to have passed the illness to family, friends or anyone at work.

When a test that could apparently prove I had contracted coronavirus first became commercially available in New York last month, I asked my doctor to send me for a blood draw. Rather than testing whether a person has an active infection, these tests perform a sort of biological archaeology, searching for pathogen-fighting proteins known as antibodies that show a person has had the illness in the past and possibly developed enough immunity to fend it off in the future.