Counterfactual evaluation of COVID-19 control policies in South Korea: A scenario-based modeling study.

BACKGROUND

The COVID-19 pandemic highlighted the importance of timely public health interventions for epidemic control. South Korea implemented vaccination, testing, contact tracing, and social distancing to limit transmission. This study evaluated the impact of these measures to inform pandemic preparedness.

METHODS

Surveillance data were used to calibrate an age-specific V-SEIQR model incorporating vaccination counts, the Q-proportion-proportion of confirmed cases already in quarantine at diagnosis, used as a proxy for contact tracing performance-testing capacity, and social distancing intensity. Scenario-based analyzes compared alternative policy timings and intensities during the pre-Delta (November 1, 2020-June 30, 2021) and Delta period (July 1, 2021-December 31, 2021) with cumulative confirmed cases as the primary outcome.

RESULTS

Advancing vaccination by two months reduced confirmed cases by 48%, indicating earlier deployment had a greater impact than faster rollout speed. Reduced testing capacity increased epidemic burden. A lower Q-proportion was associated with larger case burdens. During the Delta period, delaying the Gradual Recovery to a New Normal policy or maintaining stricter distancing longer mitigated resurgence.

CONCLUSIONS

Earlier vaccine deployment, sustained testing and contact tracing capacity, and timely adjustment of social distancing were important for epidemic dynamics. Quantifying these effects within a unified modeling framework provides structured, policy-specific evidence to support pandemic preparedness planning.