Real World Evidence of Trace, Test, Isolation, and Quarantine Impact on the COVID-19 Pandemic Response Performance

Background: There is continuing uncertainty about the effectiveness of testing, tracing, isolation, and quarantine (TTIQ) policies during the pandemic. Methods: We developed proxy indicators of the implementation of TTIQ policies at subnational and national (Republic of Korea), and international level (111 countries) from the beginning of 2020 to September 2021. These were: proportion of quarantined population (“Q-proportion”) among newly diagnosed COVID-19 cases/week, ratio of quarantined people to cases, and ratio of negative tests to new cases, with higher values suggesting more complete TTIQ. We used linear regression to analyze the association between TTIQ indicators and 1-week lagged cases and cumulative deaths, separating periods before and after vaccines becoming available. Findings: We found consistently inverse associations between TTIQ indicators and COVID-19 outcomes, with gradual attenuation as vaccination coverage rose. Q-proportion overall (β= -0·091; p -value < 0·001) and log-transformed quarantined population per case (β ranges from -0·626; p < 0.001 to -0·288; p = 0·023) in each of 9 provinces were negatively associated with log-transformed 1-week lagged incidence in Korea overall. The strength of association decreased with greater vaccination coverage. The ratio of negative test results/new case was also inversely associated with incidence (β= -1·19; p -value < 0·001) in Korea. Globally, increasing negative test ratio was significantly associated with lower cumulative cases and deaths per capita, more so earlier in the pandemic. Jurisdictions with lower vaccination coverage showed the strongest association. Interpretation: A real-world evaluation demonstrates an association between performance of testing, contact tracing, isolation, and quarantine and better disease outcomes. Funding Information: Ministry of Foreign Affairs, Republic of Korea. Declaration of Interests: None to declare.