August 3, 2021

expert reaction to news that the NHS COVID-19 app has been updated so fewer contacts of a positive asymptomatic case will need to isolate

The government have announced that changes made today to the NHS COVID-19 app will result in fewer contacts being advised to self-isolate following a close contact with a positive case, as they urge the public to continue using the app.

Prof Allyson Pollock, Clinical Professor of Public Health, University of Newcastle, said:

“What needs to happen is a clinical trial evaluating the app and cost effectiveness. So far we have only had observational studies and modelling which is unacceptable. We would not accept the efficacy of medicines and vaccines on this basis so we need thorough trial evaluation of this app.

“According to an earlier paper in the evaluation of the epidemiological impacts of the app (https://www.bdi.ox.ac.uk/publications/1176891) secondary attack proportions are 6%, i.e. for every 100 people  94 people have to self-isolate unnecessarily. There is no detail given on the cases. Crucially, current evidence is based on modelling and observational data not a trial evaluating costs, harms, benefits and effectiveness. Currently the yield of cases is likely to be much lower as prevalence is low and the number of people being pinged and told to isolate is very high.  

“We know from other PHE studies cases are more likely to be close household contacts who would have been picked up through the local outbreak control teams using more sensitive probing and communication- and which have a higher detection rate according to link above. A well designed trial would have compared the cost- effectiveness of the app with more sensitive local outbreak control teams .”

https://www.gov.uk/government/news/nhs-covid-19-app-updated-to-notify-fewer-contacts-to-isolate

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