The mystery virus that protects against monkeypox

A At the turn of the 19th Century, a bizarre medical panic swept across London. Informative pamphlets were distributed. Alarmist books were authored. Dubious treatments emerged. The public was warned, en masse, that it was in peril – at urgent risk of… morphing into cow-humans.

A small group of controversial doctors had been whipping up concerns about a pioneering medical procedure, which included taking a virus thought to infect cattle and using it to protect people against its cousin, smallpox.

The technique was named "vaccination", after the Latin "vaccinus", meaning "of a cow" – and the early evidence suggested that it was extraordinarily effective, protecting 95% of people from an infection which usually killed around 30% of its victims and permanently disfigured most of the rest. There was even an early hope that it might eventually vanquish the disease forever.