The UK's scientists have been trying to trace COVID-19's path through the population ever since the coronavirus arrived on British shores.
In what is thought to be the largest study of its kind in the world, an app developed by King's College London (KCL) and technology company Zoe, which tracks symptoms of the disease, has been downloaded more than three million times in the UK.
Not to be confused with the government's contact-tracing app, the COVID-19 Symptom Study app allows users to report daily whether they feel healthy, and record any symptoms. The scientists have been using the data to estimate how the virus may have travelled through the population.
Source: BBC News, 23 May 2020