A new study by Cambridge researchers Andrew Harvey and Paul Kattuman suggests that it is time to say “farewell to the R”, and switch to a different approach based on the growth rate of disease rather than its contagiousness. 

Published in the Journal of the Royal Society Interface, the study concludes that though the R rate is what has always been used to monitor the pandemic, it “wanes in usefulness” since it only looks at the “number of infections expected to result from a single person in a completely susceptible population.”

When pandemics enter their later stage, the R rate stops being the best way of monitoring them because it only looks at the contagiousness of the disease in a given moment. 

Instead, the researchers claim, the focus should be on the growth rate of new cases and deaths so that the disease's trajectory can be forecasted. 

Harvey and Kattuman’s findings are already being used to fight the pandemic in countries across the world. Trackers in the UK and India have been created “to identify regions of high risk and to frame containment and relaxation policies.” 

Kattuman added: “These are the numbers that really help guide policymakers in making the crucial decisions that will hopefully save lives and prevent overcrowded hospitals as a pandemic plays out – which, as we have seen with COVID-19, can occur over months and even years. The data generated through this time-series model has already proved accurate and effective in countries around the world.”