Cast your mind back to the height of the Covid-19 pandemic, when the world seemed to have a single shared obsession – the “R number”. This simple metric, which measured the reproductive rate of the virus, gave a tangible sense of the invisible threat that lurked around us. Was it above one, meaning that the virus was spreading exponentially? Or had lockdowns and other public health measures successfully brought it below that threshold? The R number became a predictor of the public mood like a barometer – forecasting impending storms, or clear skies.

Covid is very much still out there, but swift measures on social distancing, travel restrictions, and vaccine distribution mean that it’s no longer seen by most as a major threat to humankind. These policies demonstrated what fast action, strong leadership and global cooperation can achieve, but their success was judged almost entirely by that R number.