In a scenario where no social distancing was in place and 1000 new symptomatic cases were reported each day, up to 41,000 contacts would need to be quarantined each day if relying on contact tracing to achieve infection control, according to a new study published in the Lancet Infectious Diseases.
Using social-contact data on more than 40,000 individuals from the BBC Pandemic database, the modelling study simulated SARS-CoV-2 transmission in different settings and under different combinations of control measures.
The model estimated that combined isolation and tracing strategies would reduce transmission more than mass testing or self-isolation alone, with a mean transmission reduction of:
- 2 per cent for mass random testing of 5 per cent of the population each week;
- 29 per cent for self-isolation alone of symptomatic cases within households;
- 35 per cent for self-isolation alone outside households;
- 37 per cent for self-isolation plus household quarantine;
- 64 per cent for self-isolation and household quarantine with the addition of manual contact tracing of all contacts;
- 57 per cent with the addition of manual tracing of acquaintances only; and
- 47 per cent with the addition of app-based tracing only.
If limits were placed on gatherings outside of home, school or work, then manual contact tracing of acquaintances alone could have an effect on transmission reduction similar to that of detailed contact tracing.
In a scenario where 1000 new symptomatic cases meeting the definition to trigger contact tracing occurred per day, the researchers estimate that, in most contact tracing strategies, 15,000-41,000 contacts would be newly quarantined each day.