London | My eight-year-old son came into our bedroom one night this week, feeling hot. It turned out he had a slight but persistent temperature, and in the morning, a cough. Two COVID-19 boxes ticked, so he was immediately off school, and the whole family went into self-isolation.

It was most likely just a cold or mild flu, the sort of thing thousands of kids come down with when the schools go back after the summer. But the only way to avoid a 14-day confinement is to get a test and a negative result.