Frequently asked questions

What is REACT?

The REACT programme is a series of studies that are improving our understanding of how England’s epidemic is progressing. To do this, the programme is carrying out two major pieces of work that are using home sampling and testing to track the infection.

The first, REACT 1, is using at home antigen (swab) tests sent to 150,000 randomly selected people across England each month. This is examining how widely the virus has spread and how many people are currently infected with the coronavirus.

The second, REACT 2, has been assessing a number of different finger-prick antibody tests to see how accurate they are and how easily people can use them at home. Antibody tests are designed to tell individuals if they have had an immune response to the infection. These tests are offering an indication of how far the virus has spread across the country and what proportion of the population have been infected and recovered. The best performing test is being regularly sent out to hundreds of thousands of volunteers to find out how many people have already been infected.

REACT is also running a number of other studies. These include:

  • REACT Long COVID. This study is looking at biological, environmental and social factors to better understand why some people who are infected with the coronavirus have symptoms for several weeks or even months – a condition called Long COVID – while others don’t.
  • REACT GE. This is looking for biological ‘signatures’, such as molecules in the blood or variations in people’s genes, that could help explain why some infected individuals experience serious illness while others don’t.

Why are you doing these studies?

As the Government plans its ongoing strategies to control the virus, it is vital to understand how many people have been or are currently infected with the coronavirus, and who is most at risk. REACT data are helping guide policies designed to protect people and the NHS.

Measuring the presence of coronavirus antibodies in the population is helping estimate how many people have been infected with the virus, while also improving our understanding of the immune response to the virus.

Other REACT studies are also helping to better understand the illness that the coronavirus causes, and why some people are worse affected than others. This will help scientists identify new ways to support and treat people with COVID-19. 

What’s the difference between the antigen and antibody tests?

Antigens are anything that can cause an immune response in the body, like viruses and bacteria. In this case, the antigens that the REACT 1 test is looking for are bits of genetic material from the coronavirus. For the test, a person needs to take a swab of their nose and throat and send the sample off for testing in a laboratory. The lab test that detects whether coronavirus genetic material is present in a sample or not is called PCR (polymerase chain reaction). This indicates whether someone is currently infected.

Antibodies are immune molecules that the body produces in response to an infection. The tests that are being assessed in REACT 2 look for raised levels of antibodies to the coronavirus in an individual’s blood. The presence of antibodies could indicate that a person has previously been infected and has recovered from COVID-19, and could help to identify people who may be at lower risk of future infection. The test involves doing a finger prick, collecting a drop of blood onto a testing stick, and adding a few drops of a liquid that’s provided. You read off the result yourself shortly afterwards.

How accurate are the tests?

The antigen (PCR) test for coronavirus is generally considered the most accurate test to detect current infection with coronavirus.

REACT scientists have assessed the accuracy of a number of finger-prick antibody (lateral flow) tests, and we have reported the findings here. The most accurate test evaluated, Fortress, is currently being rolled out to hundreds of thousands of people roughly every 6 weeks to survey the proportion of people with antibodies in the population.

The Fortress test was found to be 98.6% specific, and 84% sensitive. This means the test can correctly rule out people who haven’t got antibodies almost 99% of the time, and can correctly identify people who do 84% of the time.

What if I get a positive result from my swab (antigen) test?

The results will be sent to the participant by post and, if positive, he or she will be asked to self-isolate along with other members of the household, in line with NHS and Public Health England advice. Those who receive a positive result will also be referred to NHS Test and Trace.

What if I get a positive result from my finger-prick (antibody) test?

We know that antibody finger-prick tests are not 100% accurate (see findings here on test accuracy).

This means a positive test result does not necessarily mean you have had COVID-19 or that you are protected from getting it again, and a negative test result does not necessarily mean that you have not had COVID-19. Whatever your test result, it is important that you continue to follow the current Government advice that applies to you. This is why we are asking participants to not take any action or choose not to take an action based on the result.

Based on previous experience with other similar viruses, the presence of antibodies most likely does confer some level of protection, although we don’t know to what extent or for how long. We hope that this study will further our understanding of this.

Why does REACT sometimes produce different results to ONS?

The REACT 1 study is tracking current coronavirus infections in the community by testing more than 150,000 randomly-selected people each month over a two-week period. The study recruits new people each month to help ensure the sample represents the wider population and offers a high-resolution snapshot of the situation across a particular time period.

This is different from the ONS COVID-19 Infection Survey which runs continuously and samples the same people over time to understand household transmission. Because the studies use different methods, this means that sometimes they report different figures.

When will the study be finished?

The REACT studies are ongoing and are regularly publishing findings.

You can read about what the study has found to date using this link

Why have I been asked to join this study?

The initial invitation was sent to your address after it was randomly selected. This random selection method ensures that the data we get accurately represents the whole country.

I’ve received a letter to join REACT but I can’t get the website to work, what do I do?

If you have been asked to take a swab test (REACT1) and you are able and willing to do so, please visit the website here, which will require you to enter your unique access code found on your invitation letter. If you are still stuck, please email our partners Ipsos MORI and their helpdesk will be able to assist. Please note this website is only for people who have been invited to participate.

If you have been asked to take a fingerprick antibody test (REACT2) and you are able and willing to do so, please visit the website here, which will require you to enter your unique access code found on your invitation letter. If you are still stuck, please email our partners Ipsos MORI and their helpdesk will be able to assist. Please note this website is only for people who have been invited to participate.

Who can I contact to get help about my involvement in this study?

We're working with our partners Ipsos MORI to conduct this study. If you have a question regarding taking part in the swab testing study, please contact them using these details:

  • 0800 157 7818

If you have a question regarding taking part in the antibody (finger-prick) testing study, please contact Ipsos MORI using these details:

  • 0800 819 9150

What will you do with my data?

This research is compliant with the General Data Protection Regulation (GDPR), a set of laws that protect your data and its privacy. All information that you give us will be treated in the strictest confidence and your identity will not be passed on to a third party other than the research team.

All of your personal data used and collected during this study will be stored by Ipsos MORI and Imperial College London in secure data centres and servers within the United Kingdom and European Economic Area.

We have taken a number of precautions to ensure that your data is safe and protected from loss, theft and misuse.

I want to participate in the research, can I sign up?

At the moment you can only take part if you have received an invitation letter. The research is being carried out with a random sample of people from across England to get a representative sample of the population, so we are not accepting volunteers. Please do not contact us at this stage if you are only looking to participate.

At a later stage, we will be recruiting more people to join REACT and may then look for volunteers. Once that stage has reached we will provide details of how to express interest in participating.

Is this a genuine study?

The REACT studies are legitimate research programmes being carried out in partnership by Imperial College London, the UK Department of Health and Social Care, and IpsosMORI. This study has received formal ethical approval from the South Central - Berkshire B Research Ethics Committee. You can find out more about the research in this news article.

My question isn't answered here

If you have further questions about either of the REACT studies, you may find further answers on the FAQ pages developed for participants by our operational partners, Ipsos MORI:

If you have been invited to take part in one of the REACT studies and still have a question, query or comment, please contact the relevant helpline team: