Success of test, trace and isolate programmes depends on speed, compliance and monitoring

The speed at which fast tests can be completed, results delivered and contact traced, high levels of public compliance and the ability to identify a large proportion of cases will be crucial to the success of any Test, Trace and Isolate (TTI) programme according to Data Evaluation and Learning for Viral Epidemics (DELVE). The multi-disciplinary group convened by the Royal Society supports a data-driven approach to learning from the different approaches countries are taking to managing the pandemic.

Research by DELVE shows that, if effectively implemented across the population, TTI can help control the UK COVID-19 epidemic as part of a wider package of interventions including social distancing, infection control, and hand and respiratory hygiene. Self-isolation of symptomatic individuals and quarantine of their household contacts as part of the TTI system, has a substantial impact on the number of new infections generated by each index case. Adding contact tracing for extra-household contacts of confirmed cases to this broader package of interventions reduces the number of new infections otherwise occurring by 5-15%.

DELVE modelling shows that the upper end of this range can be achieved when the overall test and trace period for contacts has been reduced from five days to three days, due to the quarantining of infected contacts just before they become most infectious.

The extent to which the public participate and comply with the TTI guidance strongly affects its usefulness, as there are many steps in the TTI system where cases and contacts can be lost. Bringing more contact chains within the TTI system is central to its effectiveness; integration of TTI data with systematic population-based surveillance can be mutually beneficial in focusing efforts where transmission is greatest. Phone-based apps may be able to increase TTI speed and compliance but is likely to be an adjunct to a manual TTI system. 

Anne Johnson, Professor of Infectious Disease Epidemiology at University College London, Vice President of the Academy of Medical Sciences and a member of the DELVE committee said: “All aspects of a coordinated TTI system must be firmly guided by the core public health purpose of reducing transmissions and contributing to maintaining an effective reproduction number Re below 1. Alongside its public health benefits, the system enables identification of cases for clinical care and provides intelligence on the course of the epidemic (surveillance), which in turn enables TTI to be targeted to optimise its primary purpose. Fast testing also allows those who are not infected, and their families, to carry on with their lives.

”One of the keys to success of any potential TTI programme will be ensuring that it is carried out in an integrated way – joining up Public Health England, NHSX, primary and community care and the various other strands required to deliver a truly national effort.  There are many potential pitfalls for such a system and it is important that all of those are carefully considered in introducing such a complex undertaking.”

Other key points in the report include:

• Achieving substantial increases in speed is likely to require a system-wide approach utilising existing public health infrastructure and capacity, with greater linkage to primary and community care
• Avoiding perceptions of negative consequences from engaging in TTI and actively incentivising participation will help maintain public support
• Finding people infected with COVID-19 will require detailed understanding of how incidence, prevalence and risk factors for COVID-19 vary across geography, demography and economic sectors
• Contact tracing based on confirmed cases, rather than symptoms, is most efficient, due to the large of proportion of those with symptoms not having COVID-19

Venki Ramakrishnan, chair of the DELVE committee said: “Countries that have managed to, at least temporarily, control their COVID-19 epidemics have almost all enacted and maintained substantial testing and contact tracing efforts from early in their epidemics. Our report suggests that a test, trace and isolate programme, if effectively delivered, can play an important part in bringing this pandemic under control but that it should not be considered as a silver bullet.”

The Society gratefully acknowledges the financial support of the Leverhulme Trust.

The full report can be accessed at the DELVE initiative github: https://rs-delve.github.io/reports.html