Optimal Social Distancing Policy for COVID-19 Control in Korea: A Model-Based Analysis

Abstract

Background: Since March 2020, when coronavirus disease 2019 (COVID-19) was declared a pandemic, many countries have applied unprecedented restrictive measures to contain the spread of the virus. This study aimed to explore the optimal social distancing policy for COVID-19 control in South Korea to safely reopen the society.

Methods: We developed an age-specific, deterministic compartment epidemic model to examine the COVID-19 control decision-making process, including the epidemiology of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) between 1 July 2021 and 30 December 2022. The model consists of the natural history of COVID-19, testing performance, vaccinations, and social distancing enforcement measures to detect and control SARS-CoV-2. We modelled potential intervention scenarios with three distinct components: 1) social distancing duration and level; 2) testing intensity; and 3) vaccination uptake rate. The primary and secondary outcomes were COVID-19 incidence and prevalence of severe patients requiring intensive care unit (ICU) care.

Results: Four (or more) months of social distancing (that can reduce 40-60% transmission) may mitigate epidemic resurgence and ICU demand in the future and keep the cases below the capacity limit if the testing intensity and vaccination rate remain constant or increase by 20% (with respect to the current level). In contrast, two months of strict social distancing enforcement may also successfully mitigate future epidemic surge and ICU demand as long as testing intensity and vaccination rates are increased by 20%.

Conclusion: In South Korea, given the relatively high vaccination coverage and low incidence, four or more months of social distancing enforcement can effectively mitigate epidemic resurgence after lifting the social distancing measures. In addition, increasing the testing intensity and vaccination rate may help reduce necessary social distancing levels and duration to prevent a future epidemic resurgence and mitigate social and economic damage.

Keywords: COVID-19; ICU; Pandemic; SARS-CoV-2; Social Distancing Policy.

Fig. 1. Schematic representation of the modelling approach. We use a compartmental modelling framework to incorporate (A) natural history of COVID-19 and (B) age structure. (A) Natural history was captured by modelling transition of individuals between eight states: uninfected; susceptible, vaccinated, exposed, asymptomatic (undetected), asymptomatic (true positive), symptomatic (detected), recovered, and dead. (B) The population was subdivided into four groups based on age: 0–19 years, 20–39 years, 40–59 years, 60 years and above. Population in the four groups were modelled to have different contact patterns. As we focused on the key intervention strategies such as social distancing duration/level, testing rate and vaccination rate, we varied the parameters beta, tau, and v for respective intervention scenarios.

COVID-19 = coronavirus disease 2019.

Fig. 2. Projected incidence of COVID-19 in South Korea between November 2021 and December 2022. The impacts of possible COVID-19 response scenarios were compared. The black dashed line indicates the time of projection (21 November 2021) and the red dashed line indicates the time of lifting social distancing control (in 2, 3, or 4 months). The pink shaded area projected results with 95% confidence intervals by varying transmissibility, testing intensity and vaccination rate. (A) Scenario 1 (base case: 3 months of moderate social distancing control with current level of testing and vaccination rates); (B) Scenario 2 (4 months of strict social distancing control with current level of testing and vaccination rates); (C) Scenario 3 (2 months of strict social distancing control with 20% increased level of testing and vaccination rates than the current rates); (D) Scenario 4 (4 months of weak social distancing control with current level of testing and vaccination rates); (E) Scenario 5 (2 months of weak social distancing control with 20% increased level of testing and vaccination rates than the current rates).

COVID-19 = coronavirus disease 2019.

Fig. 3. Projecting prevalence of severe patients in South Korea between November 2021 and December 2022. The impacts of possible COVID-19 response scenarios were compared. The black dashed line indicates the time of projection (21 November 2021) and the red dashed line indicate the time of lifting social distancing control (in 2, 3, or 4 months). The pink shaded area projected results with 95% confidence intervals by varying transmissibility, testing intensity and vaccination rate. The light blue shaded area indicates the ICU capacity for COVID-19 patients in South Korea. (A) Scenario 1 (base case: 3 months of moderate social distancing control with current level of testing and vaccination rates); (B) Scenario 2 (4 months of strict social distancing control with current level of testing and vaccination rates); (C) Scenario 3 (2 months of strict social distancing control with 20% increased level of testing and vaccination rates than the current rates); (D) Scenario 4 (4 months of weak social distancing control with current level of testing and vaccination rates); (E) Scenario 5 (2 months of weak social distancing control with 20% increased level of testing and vaccination rates than the current rates).

COVID-19 = coronavirus disease 2019, ICU = intensive care unit.

Fig. 4. Cumulative incidence of COVID-19 cases and the peak number of severe COVID-19 patients in South Korea between 1 July 2021 to 31 December 2022. This heat map displays the cumulative incidence of COVID-19 cases (A) and the peak number of severe COVID-19 patients (B) between 1 July 2021 to 31 December 2022. Each panel corresponds to the social distancing duration (2, 3, 4 months from 22 November 2022), social distancing control level (strong as reducing 60% transmissibility, medium as reducing 50% transmissibility, and weak as reducing 40% transmissibility), testing rate (base as the average daily testing rate between 1 July 2021 to 21 November 2021, ×0.8 as 20% decrease of the average rate, and ×1.2 as 20% increase of the average rate), and vaccination rate (base as the uptake rate by the current vaccine roll-out plan, ×0.8 as 20% decrease of the current rate, and ×1.2 as 20% increase of the average rate). Rt base corresponds to the current average transmissibility between 1 July 2021 to 21 November 2021 and Rt base ×3 and Rt base ×4 as the 3 times and 4 times increase of the current level of transmissibility from 22 November 2021 to 31 December 2022.

COVID-19 = coronavirus disease 2019, ICU = intensive care unit.