The coronavirus behind covid-19 has infected most people in the world, killing around 15 million people and leaving about 400 million individuals with long-term health problems. It also caused the biggest economic downturn since the Great Depression of the 1930s. Despite all this, it could have been much more devastating.

“On the scale of pandemics, covid-19 was moderate,” says Mark Woolhouse at the University of Edinburgh, UK. “There will be others, and they very easily could be an awful lot worse than the one we had. This…