Stuck at home last weekend, I cleared out some old boxes and stumbled on a collection of long-forgotten letters. I wrote them back in 1985 and they were dispatched to my family in the UK from a hospital in a tiny town called Kunri, in the Sindh region of Pakistan. I spent several months there volunteering for a healthcare project between school and university.

The letters’ message was oddly relevant. Like most suburban, middle-class, western teenagers, I had grown up hugely complacent about infectious disease. In 1970s Britain, vaccinations seemed so efficient at stopping nasty illnesses that I never gave the issue a moment’s thought (except when joking that I hated needles).

In Kunri, my complacency was shattered. Soon after arriving, I noted in an old-fashioned blue “airmail” letter that I had been shocked to see children suffering from polio. The disease was rampant in the region (and had paralysed 350,000 primarily young people across the world at that time, according to the Gates Foundation).