As part of measures to help control the spread of coronavirus, the UK government has introduced a track and trace system.
The new NHS Test and Trace scheme has been launched in England on Thursday (28 May), with thousands of contact tracers now starting to make their first phone calls to people deemed at risk of coronavirus infection.
What is contact tracing?
Contact tracing is a long and laborious process that has been likened to detective work.
It is carried out by public health officials and involves interviewing a patient to identify anyone who they have recently had close contact with.
Health officials then alert these people that they may have been exposed to a virus, and often encourage them to quarantine themselves so as to avoid any further spread.
Contacts who are considered to be particularly high risk are intensely monitored to identify any signs of infection.
When will tracing be ready in the UK?
The new NHS Test and Trace scheme is now up and running in England, with the help of 25,000 contact tracers.
Under the new system, NHS tracers, or local public health teams, will text, email or call people who test positive with coronavirus and ask them to share details of those they have been in close contact with, along with places they have visited.
These contacts will then be considered to be at risk of infection and be instructed to self-isolate at home for 14 days as a result, even if they are not displaying any symptoms.
Anyone who has already had the virus will also be asked to self-isolate.
An accompanying app for the tracing system in England is still facing delays of several weeks, although trials began on the Isle of Wight on 5 May.
The government hopes the system will be ready to be used more widely across England in June, although an official date it will be available has not yet been confirmed.
A test and trace system is also launched in Scotland on Thursday (28 May), which comes as First Minister Nicola Sturgeon is expected to announce an easing of some restrictions on Thursday afternoon.
In Northern Ireland, a telephone contact tracing system is already in place, while in Wales the government wants its “test, trace, protect” programme to be operational by the end of May.
How will the app work?
Smartphone users will be able to download the app and opt-in to record their symptoms if they start to feel unwell.
A warning alert is then sent to others who they have been in close contact with, and also have the app, via Bluetooth signals.
If a person is then confirmed to have been infected by coronavirus, a red signal will be sent to other app users they have been in close contact with.
Currently, the app either tells users: “You’re OK now”, or “You need to isolate yourself and stay at home”.
Essentially, the app aims to identify exactly who needs to self-isolate and who doesn’t, thereby making it easier to lift social distancing measures.
Why is contact tracing important?
Health Secretary Matt Hancock said the contact tracing operation would be functioning in a “matter of weeks”, and said both mass testing and contact tracing are “crucial to holding down the rate and level of transmission of the disease”.
Through a process of mass testing, combined with isolating infected people and their contacts, ministers hope that any future localised outbreaks of the virus can be kept under control.
Both mass testing and contract tracing don’t necessarily need to be in place before the current restrictions are eased, but Mr Hancock said contact tracing works better when the number of infections is low.
He said: “The truth is that we need to get the number of new cases down, right down, and the lower you go, the more effective contact tracing is because the more resources you can put into each individual case that gets a positive test.
"You can really make sure you can get hold of all of their contacts and get them, in many cases, to self-isolate.
"The smaller the number of new cases, the more effective the test, track and trace system will be."
How has contact tracing worked in other countries?
Several countries around the world have implemented mass contact tracing in an effort to track and trace the spread of the virus. These are some of the measures in place:
People are given a QR code and an app which classifies them as green, amber or red, with their health status determining where they are allowed to go and what they can do.
Authorities have traced people’s movements rigorously after testing positive, through means including interviews, GPS tracking, credit card records and surveillance camera footage.
Once potential virus carriers are identified they are also tested and anonymised data of coronavirus patient’s movements is published online, enabling others to see if they may have come into contact with anyone who is infected.
Known as the Covid-19 Smart Management System, it is run by the country’s Centers for Disease Control and Prevention and can analyse a person’s movements in just 10 minutes.
The government is able to trace between 2,000 and 4,000 contacts of coronavirus patients per day, with police and army officers phoning people who may have come into contact with a confirmed case.
On March 20, the country launched the TraceTogether app to track the contacts of those who have been infected, and it claims to have around 1.1 million users - around one fifth of the country’s population.
The app logs unique codes via Bluetooth signals between nearby phones that have it installed.
Every person in Germany who has come into contact with an infected patient in the period of two weeks is tracked down and tested, using a smartphone app developed for the Robert Koch Institute.
French authorities will implement mobile teams to trace the contacts of people infected, although have not yet specified how many tracers it currently has.
The country aims to test 700,000 people per week and begin lifting restrictions on 11 May.
The government plans to launch a contact tracing app later this month, which will warn smartphone users if they come into contact with anyone infected with coronavirus.
The US currently has 2,200 contact tracers, according to a report by the Association of State and Territorial Health Officials, although it is estimated it will need an additional 100,000 to trace possible infections.
At present, contact tracing is being conducted at a state level.
Mike Bloomberg, the former mayor of New York City, is helping to build an "army" of coronavirus tracers to test, trace and isolate residents with the virus in the tri-state area, encompassing New York, New Jersey and Connecticut.
New York state currently has 500 tracers.
San Francisco has also launched a pilot program linking a tech company with 250 tracers, while Massachusetts has said it will hire around 1,000.
Contact tracing will begin in Northern Ireland next week, after being stopped last month based on “sound public health considerations”.
Chief medical officer Dr Michael McBride said that tracing will become “crucially important” to overcome local pockets of infection.
A team of 2,000 contact tracers will be distributed regionally to track the spread of coronavirus.
A total of 200 will be in Brussels, 600 in Wallonia and 1,200 in Flanders, according to the national newspaper De Tijd.
Those who are identified by the tracers will then be tested and quarantined for two weeks if they test positive.
Federal authorities are also working on developing an app to locate people potentially infected with the virus.