LONDON — More than 500,000 people in Britain were told to self-isolate last week by the government-backed Covid-19 Test and Trace app, with similar numbers expected over the coming weeks.

In the week ending July 7, a record 520,194 people in England were alerted by the app that they had been in close contact with someone who had tested positive for coronavirus, and therefore needed to self-isolate.

A BBC analysis found last week that as many as 4.5 million people in the U.K. could be instructed to self-isolate by the Test and Trace system between mid-July and the policy change on August 16.

Research published in the British Medical Journal in late June studied the interactions of 5,802 people over 14 days, finding that the average participant had 59 interactions that could be defined as close contact. The study found that for every infected person, an average of 36 close contacts would be able to be identified and contacted, which could mean millions are currently being told to self-isolate.

Earlier this week, British media reported that Covid app users were being "pinged" and told to self-isolate when their neighbors contracted the virus, with the technology underpinning the app's Test and Trace system detecting "close contact" with positive cases through the walls of their homes.  

Currently, anyone in the U.K. who is told a close contact has tested positive for Covid is required to self-isolate at home for 10 days. People may be contacted via phone, email or text by the NHS Test and Trace system, or via a notification on the app.

"Close contact" is defined in the U.K. as spending 15 or more minutes within two meters of an infected person.

British Health Minister Sajid Javid recently announced that from August 16, people who had been fully vaccinated against Covid would no longer be required to self-isolate if a close contact had tested positive for the coronavirus. The change in policy would also apply to children under the age of 18.

Employee absence concerns

England is set to lift almost all of its remaining Covid restrictions on Monday, which Prime Minister Boris Johnson has said will be an "irreversible" move.

However, the country is currently experiencing a rise in new cases of the virus, which has been linked to the highly transmissible delta variant.

There were 48,553 new cases of the virus in the U.K. on Thursday, bringing the country's total number of confirmed cases since the beginning of the pandemic up to 5,281,098.

Rising case numbers have prompted concerns among industry leaders that the contact tracing system could create employee shortages.

Karan Bilimoria, president of the Confederation of British Industry — which represents 190,000 businesses — said in a statement on Thursday that the government should bring forward the rule changes for self-isolation.

"Infection rates may be increasing rapidly but it's clear the test and trace system needs an overhaul, with over two-thirds of the adult population now fully jabbed," he said.

"As more businesses prepare to open their doors on Monday staff shortages are being felt acutely across all sectors in all areas of business particularly across our struggling sectors in hospitality and leisure."

Nick Allen, CEO of the British Meat Processors Association, told the BBC on Friday that some organizations may be forced to close production lines, with up to one in 10 meat production workers being asked to isolate by the app.

Meanwhile, it was reported on Monday that passengers flying from Terminal 5 of London's Heathrow Airport faced disruption after a number of employees were told to isolate by NHS Test and Trace.

Up to 900 workers — more than one in 10 employees — at Nissan's manufacturing plant in Sunderland, England, are currently absent from work after being "pinged" by the app, the BBC reported on Thursday.

Deleting the app

A poll conducted by Savanta ComRes for the Guardian newspaper, published Tuesday, found that more than one in three adults aged 18 to 34 had already deleted the NHS app. Around one in five adults of all ages said they intended to delete it within a week, according to the survey.

Government figures and health authorities have urged the British public not to delete the app.

A spokesperson for the U.K.'s Department of Health and Social Care told CNBC via email on Friday that the NHS Covid app had prevented an estimated 600,000 infections and 8,000 deaths between September and December.

"The app is doing exactly what it was designed to do — informing close contacts of someone who has tested positive for Covid-19 that they are at risk and advising them to isolate," they said.

"As cases continue rising it is vital people are aware of their personal risk so they can make informed decisions on their behavior to protect those around them." 

Giving evidence in Parliament last week, Jenny Harries, chief executive of the U.K. Health Security Agency, said work was underway to "tune" the app so that would take vaccination status into account.

"It is important at the moment to remind people how important it is to keep the app running," she said.

The NHS app, which has been downloaded more than 26 million times, is not mandatory and there is no legal obligation for users to self-isolate if they are "pinged."