In a desperate effort to encourage people to self-isolate when pinged by the NHS Covid app or contacted by Test and Trace – even cancelling their wedding day if necessary – the Prime Minister’s official spokesman said yesterday that: “One in three people contacted either by Test and Trace or the app go on to develop coronavirus.”
There’s just one problem with this latest nugget of fear-based nudgery: it’s not true.
Test and Trace get in touch with people’s contacts and ask them to self-isolate. The proportion of those contacts who become infected is known as the secondary attack rate (SAR). Public Health England publishes the data on this SAR from Test and Trace data in its Technical Briefings, so we know what it is. The most recent estimate for the SAR of the Delta variant (in June) is that 10.3% of an infected person’s household contacts become infected (the SAR for non-household contacts is considerably lower).
How, then, can it be true that one in three – 33% – of people contacted by Test and Trace or the app go on to develop coronavirus? That’s claiming the SAR of SARS-CoV-2 is around 33%, but the Government’s own published data says it’s more like 10%.
Can the Government back up its claims, and explain why it is stating that the SAR of Covid is more than three times the figure published in its own data?