Epidemiology of the NHS COVID-19 app: design, evaluation, and future considerations

Testing, tracing, isolating, and quarantine (TTIQ) are the mainstays of the initial response to a new pathogen. The extent to which they mitigate epidemic spread depends on the reproduction number R and on the extent of pre-symptomatic transmission, as well as on many logistical and behavioural factors.

Early analysis of SARS-COV-2 indicated that the effect of TTIQ might be limited due to extensive pre-symptomatic and pauci-symptomatic transmission. We proposed that the use of digital contact tracing could enhance the speed and reach of TTIQ policies and supported the resulting NHS COVID-19 app through its design, deployment, and evaluation.

In this seminar, Dr Fraser will describe each stage, starting with how epidemiology fitted into a range of design considerations, resulting in many countries adopting the decentralised exposure notification system co-implemented by Google and Apple. Covering the deployment stage, he will describe insights from the analytic programme which gave real-time insights into the utility of the app, and broader insights into the unfolding epidemic, new variants, and the behavioural response of the population. In the evaluation stage, Dr Fraser will present estimates of the number of cases averted, which likely number over a million in the pre-vaccine phase of the epidemic and emphasise methodological aspects. He will present estimates of the risk of transmission by duration and proximity of contact and estimates of the population distribution of risk. Finally, in lessons learnt, he will explore how this intervention might be improved for response to future emerging infections, comparing the NHS app to that used in other countries.