You should download the app even if you've tested positive for coronavirus before, or think you may have had it. If you've had coronavirus, you probably have some immunity to it, which means you may not get infected again for a while. However, it’s not clear how long your immunity will last, so it’s possible that you could still become infected. Also, if you come into contact with an infected person, you could get the virus on your belongings and pass it on.
Downloading the app will help protect your family, friends and those in your community as well as yourself. This is because the app supports the NHS's wider programme to stop the spread of the virus. The quicker we can stop the spread of the virus, the sooner we can get back to a more normal life.