REACT-1 is one of the largest population surveillance studies in the world. It measures the prevalence of SARS-CoV-2, the virus that causes COVID-19, in the general population in England. Each month, more than 100,000 people are invited to take part. Individuals are randomly selected from across all 315 local areas in England to make sure the sample represents the wider population.

Participants are sent nose and throat swabs which are then analysed in a laboratory to detect genetic material of the virus that causes COVID-19, a PCR test. The data are used to estimate how many people are currently infected across the whole population, and to calculate the R number, a measure of how quickly the virus is spreading. The study also identifies which people are more likely to be infected, and can estimate the effectiveness of vaccination against infection.

The findings provide the Government with a better understanding of the virus’s transmission, the groups most at risk, and informs public health policy.

Find all the latest publications from REACT-1 on our reports page.

REACT-1: REACTing to COVID - Imperial College London and Ipsos MORI


In April 2020 the UK Government’s Department of Health and Social Care initiated the REal-time Assessment of Community Transmission (REACT-1) programme, an unprecedented real time population study into the prevalence of COVID-19 across England. To date almost 2 million people have been tested with more than 8.5 million invitations sent out.


Information for study participants

Study participants can access more information about the personal data we collect and how we use it using the following link: React-1 Privacy Notice

If you gave permission for Imperial College London to link your health data held by NHS Digital and other NHS bodies to your survey data, we will bring data from March 2015 into the REACT cohort. We will continue to link your data into the future. You have the right to withdraw your consent to our processing of your personal data, please see the privacy policy for details.