These are unprecedented times. We are living through the biggest public health threat in living memory, yet as the NHS and policymakers grapple with the impact of the covid-19 pandemic, they lack crucial information to slow the spread and allocate limited resources. 

First of all, we still don’t have a clear picture of the full spectrum of covid-19 symptoms, particularly mild cases. While some symptomatic patients who seek medical care or are hospitalised are being tested for the virus, there are many more in the community who are wondering whether their mild cough, chest tightness, strange headache or loss of taste is actually coronavirus or nothing more than a seasonal cold. There appears anecdotally to be a wide range of mild symptoms being reported, and we need to see if they group together or are merely anxiety or other conditions like allergy. Without tests for past history, it is vital that we can understand the true symptoms of the disease to identify and isolate those who are infected as quickly as possible, without unduly burdening those who are not. 

Secondly, although the elderly and those with pre-existing conditions are more likely to get severe disease and require hospitalisation, some have only mild symptoms, and some young people can conversely get very sick. There is an urgent clinical need to discover why some patients progress rapidly while others remain asymptomatic or only mildly affected. 

As a rapid solution to this problem, my colleagues and I at King’s College London and Guys and St Thomas’ have been working with the health data science company ZOE to create a simple symptom checking app called COVIDradar. This app directs users to quickly and easily record information about their health on a daily basis, including temperature, tiredness, and symptoms such as coughing, breathing problems or headaches.

Initially, we developed the app for use within Twins UK—a cohort study of more than 15,000 identical and non-identical twins that we have been running over the past three decades. Not only do we have deep genotyping and phenotyping on thousands of these twins—including immune profiling, medical history, and microbiome analysis—they are an enthusiastic and engaged group of research participants. We wanted to quickly link the virus to this wealth of background data. We can also do the same with larger cohorts like UK Biobank

However, we quickly realised that the app would also be of great benefit to the wider public, so we have made it freely available to all. We will be making the app data available to policymakers, NHS services and academic researchers on a strictly non-commercial basis. As well as helping us understand more about the symptoms of coronavirus and the people who are most at risk of becoming seriously ill, this information will also reveal how fast the disease is spreading and identify geographical hotspots.

Importantly, this data can also help to highlight who needs testing for current or past coronavirus infection. If 50 percent of the population turn out have been affected mildly this has important ramifications. By getting live updates decision-makers can plan and allocate limited NHS resources more efficiently, and monitor the impact of policy measures such as social distancing.

The initial response to the COVIDradar app has been phenomenal. Within six hours of launching, more than 20,000 people had logged their health status. Just two days later we had more than 1.5 million users and the number is continuing to rise. We have already shared the data with the government and NHS on a million people and are also working hard to bring the app online in the US and other countries, to aid their response to this global threat.

Gathering accurate information about the symptoms and spread of covid-19 across the UK is essential if we are to slow the march of the disease and protect the NHS. By engaging millions of citizen scientists through a simple data-gathering app, we can all play our part from the relative safety of our homes. Please spread the word to your patients! 

Tim Spector is Professor of Genetic Epidemiology and the director of the Twins UK study at King’s College London @timspector. To download the app go to COVIDradar.org or covid.joinzoe.com and follow the links to the Apple App store or Google Play. 

Competing interests: TS has a published a book on food called The Diet myth (2015), and Spoon Fed (2020). The COVIDradar app is non-commercial and neither TS, Zoe, nor KCL make any money from it. TS is a co-founder of Zoe and has a financial interest in diet related pieces.