Fully vaccinated people who are pinged by the NHS Covid app are three times less likely to go on to test positive than the unvaccinated, figures show, ahead of a rule change next week that will allow the double jabbed to avoid isolation.

       From Monday, people in England who have had both jabs will no longer need to quarantine if they come into contact with a person with coronavirus.

       New analysis from the King’s College ZOE app shows that the change is unlikely to lead to a spike in cases, because those who are fully vaccinated are far less likely to go on to develop an infection, even if they come into contact with a carrier.

       The figures show that fewer than nine per cent of vaccinated people who are pinged by the NHS app go on to test positive, compared to nearly 30 per cent of the unjabbed.

       When data from the Protect Scotland app were included it dropped to just 2.4 per cent for those who had been fully vaccinated.

       Older less likely to test positive than younger

       The data also show that older people are far less likely to test positive than younger people, which is likely to be due to a combination of vaccination status, mobility and contact patterns.

       A person over 75-years-old has less than five per cent chance of testing positive after being pinged compared with nearly 22 per cent for the 17 to 25-year-olds.

       The results suggest that the vast majority of older and vaccinated people are needlessly quarantining.

       However, experts at King’s College warned that the risk of testing positive rose considerably for people suffering symptoms of Covid, even if they were fully vaccinated.

       The positivity rate for fully vaccinated people with symptoms who were pinged was nearly 30 per cent. For unvaccinated people it rose to more than 50 per cent.

       New rules explained

       Professor Tim Spector, lead scientist of the ZOE app, said: “On Thursday, the Health Secretary announced fully jabbed Covid contacts won’t need to self-isolate from August 16.

       “While I welcome efforts to address the ‘pingdemic’, cases are still very high and our research shows that whatever your vaccination status, if you have one of possible 20+ Covid symptoms recognised by ZOE, not just the classic three, you should be cautious, self isolate and get a test.”

       The ZOE results also show that far more people were likely to test positive after being pinged in Scotland than in England or Wales.

       The NHS app uses a risk-scoring algorithm to measure signal strength between phones every 3.6 minutes and gauge how often someone has come within one metre of another person throughout the day.

       In contrast, the Scottish app uses a simpler formula which pings people if they were in close contact of 15 minutes or longer.

       Analysis found that participants reported being “pinged” by the NHS app in England and Wales were around four times more likely to have Covid-19 than the general population.

       Fall in use of the app

       However, for participants in Scotland, those who reported being “pinged” by the Protect Scotland app were 10 times more likely to have an infection.

       Figures released this week show that the number of people using the NHS Covid-19 app has declined considerably following the “pingdemic” chaos, which led to hundreds of business closures.

       Data show that the app was used just 1.7 million times last week to check into venues, down 75 per cent from two weeks ago, when there were 6.7 million inputs.

       The NHS app algorithm was tweaked earlier this month to avoid pinging people who had come into contact with an asymptomatic coronavirus carrier more than 48 hours before they tested positive.