Digital twin simulation modelling shows that mass testing and local lockdowns effectively controlled COVID-19 in Denmark

Abstract

Background: Following the COVID-19 pandemic, it is important to evaluate different mitigation strategies for future preparedness. Mass testing and local lockdowns were employed during the Alpha wave in Denmark, which led to ten times more tests than the typical European member state and incidence-based restrictions at the parish level. This study aims to quantify the effects of these interventions in terms of hospital admissions and societal freedom.

Methods: This study assesses the effectiveness of these strategies via counterfactual scenarios using a detailed, individual-based simulation model that replicates the entire Danish population. The model considers multiple factors, including evolving societal restrictions, vaccination roll-out, seasonal influences, and varying intensities of PCR and antigen testing across different age groups and degree of completed vaccination. It also integrates adaptive human behavior in response to changes in incidences at the municipality and parish levels.

Results: The simulations show, that without mass testing in Denmark, there would have been a 150% increase in hospital admissions, and additional local lockdowns equivalent to 21 days of strict national lockdown. Without the policy of local lockdowns, hospitalizations would have increased by 50%.

Conclusions: In conclusion, the combination of mass testing and local lockdowns likely prevented a large increase in hospitalizations while increasing overall societal freedom during the Alpha wave in Denmark. In future epidemics, mass testing and local lockdowns can likely prevent overwhelming healthcare systems in phases of high transmission and hospitalization risks.

Fig. 1. Daily hospital admissions and societal openness in four simulated scenarios.

a The number of daily admissions to hospital. Observed development (solid black line) is shown as weekly averages to avoid weekend effects. The four scenarios, shown as colored bands, indicating the minimum and maximum of 100 simulation runs. At the bottom, the percentage of fully-vaccinated individuals is shown in color, ranging from 0% at the start of the study period to 26% at the end of the study period. b The degree of societal openness. Actual societal openness is shown as the solid black line. The colored bands indicate simulation results from the four scenarios with the median societal openness of 100 simulations highlighted. At the bottom, the observed fraction of SARS-CoV-2 Alpha cases are shown in green ranging from 0% (transparent) to near 100% (opaque), by the end of the study period it decreases as it is being replaced by Delta. Annotations only denote changes in school openings, but several other changes in restrictions have occurred during this period. For a comprehensive list of changes in restrictions, refer to. Note that openness starts at 0.47 with strict nationwide lockdown in January and goes to 1 in mid June, a reduction of 53%.