Sources say the error undermined the main function of the app and means that thousands of potential close contacts who were at risk of infection were not identified or interviewed during the week until October 6.
Nearly 19,000 fewer positive tests have been loaded into the app by patients since September 29, after NHS Direct officials condensed information for patients into a single text message, with instructions for entering the result of the positive test near the bottom of a single long message.
This change was made to reduce the number of SMS messages sent by Test and Trace in order to reduce costs.
The Covid-19 app uses the positive test result to verify the location of the user and any phone near people who may be infected. They then receive an alert and are invited to self-isolate to break the chain of transmission.
The insider believes the change was a mistake that didn’t appreciate the impact it could have if people didn’t respond to the prompt to add their test result to the app.
While less risky, the number of negative test results entered into the app between September 29 and October 6 was nearly halved, from 162,000 to 87,499.
A source close to the operation of Test and Trace confided The independent: “This change was made to save money, by reducing the number of text messages sent to people. But the unintended consequence was that people didn’t see the important code in a really long text message and meant that they probably weren’t entering their positive test code into the app.
It comes after 43,000 people falsely received a negative PCR test result despite actually being infected with Covid-19 since early September after errors from a private lab that has since been suspended by Test and Trace.
Overall, Covid infections in the UK are on the rise with around one million infections in the ONS’s latest weekly survey on Friday, with around one in 10 children infected.
UK Health Security Agency officials have noticed the drop in downloads of positive tests to the app and changes have been made to the text messages to move the instructions higher in the text.
Changes are monitored to assess their impact.
A UKHSA spokesperson said: “We are constantly reviewing our communication. Anyone who tests positive for the coronavirus should enter their result code into the app to let others know they may be at risk. “