Maths tells us the epidemic can be stopped

There is one core mathematical truth in infectious disease epidemiology: If each infected individual infects on average less than one other person (reproductive number R<1), the epidemic declines. If each infected person infects on average more than one person (R>1), the epidemic grows exponentially. Interventions designed to stop the spread of the epidemic will therefore be successful if they achieve a reduction of R to below 1.

We re-estimated key parameters of the Covid-19 epidemic, built a mathematical model of transmission, and came to the conclusion that the epidemic can be stopped if isolation of infected individuals and quarantining of their contacts is sufficiently fast, sufficiently effective, and happens at scale. We published a paper in Science describing this work.



Manual contact tracing is a valuable component of test and trace strategies. However, when an epidemic is growing exponentially, this method alone rapidly stops being able to cope with the increase in the number of cases, lacking speed, efficiency and scalability. Our calculations show that effective tracing can still be achieved with the help of a contact tracing mobile app if used by a sufficiently large proportion of the population.

Using a mobile app to register if the user has been in close contact with other app users poses many ethical challenges which need to be resolved before an app can be used. We briefly address this in our Science paper and we discuss this more extensively in our ethics paper.

Below is a graphical overview of the Science study and the results.