Christophe Fraser of Oxford’s Big Data Institute, who advises the UK’s NHS COVID-19 Tracing app, and Prof Oliver Pybus discuss the opportunities and challenges of successfully applying new technologies to pandemics past, present, and future. The COVID-19 pandemic has become a defining event of the 21st century. New technologies such as ubiquitous smartphones and virus genome sequencing offer powerful new ways to understand virus transmission and to tackle the problem of epidemic spread. But can those new tools be deployed fast enough to make a real difference to public health? And can we balance the need for privacy with the life-saving benefits of understanding how transmission occurs?