Table 1.

COVID-19 transmission scenarios and implementation of CT activities, from the WHO guidance for contact tracing, 1 February 20216

Epidemiological scenario	CT activities
No cases	Identifying and training existing personnel and preparing them for deployment and response.
Sporadic cases	Exhaustive strategies should be implemented. Case investigation for all cases is necessary for timely suppression of transmission.
Clusters	CT is required to suppress transmission within clusters and recognise events that contribute to transmission. These events can be mitigated by different Public Health and Social Measures.
Community transmission (including four subcategories of increasing incidence)	Despite challenges, CT remains crucial, particularly in high incidence scenarios. CT should continue and focus on high-risk exposure contacts in accordance with the available capacities