The number of people contacted after testing positive in England through NHS Test and Trace has now reached almost 2.7million.
They include more than 172,000 who tested positive for coronavirus in the last week of January.
What is test and trace?
Test and trace, or contact tracing, is a system for identifying people who have been in close contact with someone who has caught Covid. Almost 5.5 million close contacts have been reached so far.
Those people are then asked to self-isolate for 10 days - even if they have no symptoms - to prevent the chance of passing the virus on, if they have it.
Each UK nation has its own contact tracing service:
How does it work?
People who have tested positive for coronavirus are contacted by app, text, email or phone.
They are asked to log on to a website and give personal information, including:
- name, date of birth and postcode
- who they live with
- places they visited recently
- names and contact details of people they have recently been in close contact with
Close contacts are:
- people you've spent 15 minutes or more with - at a distance of less than 2m (6ft)
- sexual partners, household members or people you have had face-to-face conversations with - at a distance of less than 1m
Contact must have taken place within a nine-day period, starting 48 hours before symptoms appeared.
What happens if I am contacted?
If you are approached because one of your contacts has tested positive, you must stay at home for 10 days from your last point of contact with them.
You must self-isolate, even if you don't have symptoms.
Others in your household don't have to self-isolate unless they also develop symptoms, but must take extra care around you regarding social distancing and hand washing.
What about the contact tracing app?
There is also an NHS Covid app for people in England in Wales, which you can download on a smartphone (but not on smart watches or tablets).
Phones must have:
- Android 6.0 (released in 2015) or iOS 13.5 (released in 2020)
- Bluetooth 4.0 or higher
- Some recent Huaweis will not load the app
The government estimates that there are currently 16.5m active users of the app.
What can the app do?
When two phones running the app are near each other, they will make contact through Bluetooth.
If they are close for a long enough time, and one of the two owners later shares a positive coronavirus test via the app, then the other will receive an alert.
You can also use the app to check in at venues - for instance, shops or places of worship.
In total, the app has told 1.7m people to self-isolate, although some of those people may also have been reached by contact tracers.
How is the tracing scheme going?
The prime minister claimed the UK's test and trace system would be "world-beating". But it has encountered several problems along the way.
- Difficulty monitoring how many people self-isolate for the full 10 days with estimates ranging from 12% to 80%
- Delays in getting the app up and running
- Questions over whether people told to self-isolate and miss work were given enough support
The NHS Test and Trace's head, Baroness Harding, has claimed that the programme is now having a "material impact" on lowering the R number in England.
Research suggests the app alone has prevented up to 600,000 coronavirus since its launch.