Which preventive control measure initiated the “flattening of the curve”

Abstract

Summary Background When a country introduces different COVID-19 control measures over time, it is important to identify the specific measure that was effective and therefore responsible for “flattening the curve”. This information helps policymakers find the right decision and saves the economy by avoiding severe yet ineffective measures. Objective This paper aims to fill the literature gap by investigating two regions that introduced two or three consecutive measures during the second COVID-19 wave, namely Austria and Victoria. Method We calculated the first derivative (acceleration) of the filtered daily case data and identified the date of the start and end of the acceleration’s major downturn (effective phase) relative to the date when the control measures were introduced (Austria: soft/hard lockdowns; Victoria: stages 3/4 lockdowns, mask order). Results In Austria, the effective phase started 5 days after the introduction of the soft lockdown and ended at the start of the hard lockdown. In Victoria, the effective phase started 19 days after the introduction of the stage 3 lockdown, 5 days after the introduction of the mask order, and ended 6 days after the start of the stage 4 lockdown. Conclusion Considering that the effect of control measures is expected the earliest one serial interval after their introduction, the control measure responsible for “flattening the curve” was the soft lockdown in Austria and the mask mandate in Victoria. The severe lockdowns in both regions were ineffective.

Editorial Comment

“…Countries such as Singapore, Iceland, Germany, Switzerland, and Austria have implemented contact tracing programs to identify and monitor individuals who have come into contact with infected individuals [116][117][118][119][120][121]. Countries such as Taiwan, Singapore, Austria, Israel, and India have implemented mandatory mask-wearing, which has been shown to reduce the transmission of respiratory droplets from infected individuals [123][124][125][126][127][128][129]. Additionally, countries such as Singapore, Japan, and Greece have promoted good hygiene practices and encouraged social distancing, which has helped to prevent the spread of the virus [130][131][132].…”

Retrospective Evaluation of the Effectiveness of COVID-19 Control Strategies Implemented by the Victorian Government in Melbourne—A Proposal for a Standardized Approach to Review and Reappraise Control Measures

“…Although noted as complicated, there is a simplicity to this process regarding assessing whether the control measures were implemented at the right time and to what extent they actually and effectively contributed to flattening the curve (Figure 1a). The curve to be flattened corresponds to the cumulative case data of a single COVID-19 wave, whereas the first derivative of the cumulative data constitutes the daily case date (the velocity data) [11,12], i.e., the speed that the virus is spreading (Figure 1b). The first time derivative of the velocity data determines the acceleration [11,12] (Figure 1c) of the cumulative case data.…”

“…The curve to be flattened corresponds to the cumulative case data of a single COVID-19 wave, whereas the first derivative of the cumulative data constitutes the daily case date (the velocity data) [11,12], i.e., the speed that the virus is spreading (Figure 1b). The first time derivative of the velocity data determines the acceleration [11,12] (Figure 1c) of the cumulative case data. The acceleration time curve has two distinct markers-namely, the maximum and minimum acceleration peaks (Figure 1c), which define the beginning and the end of the effective phase, and it is in this time window that the acceleration shows a negative slope [11,12].…”

“…The first time derivative of the velocity data determines the acceleration [11,12] (Figure 1c) of the cumulative case data. The acceleration time curve has two distinct markers-namely, the maximum and minimum acceleration peaks (Figure 1c), which define the beginning and the end of the effective phase, and it is in this time window that the acceleration shows a negative slope [11,12]. During the effective phase, the curve of the cumulative cases flattens out (Figure 1a), which is the outcome that the implementation of control measures is supposed to achieve.…”

“…During the effective phase, the curve of the cumulative cases flattens out (Figure 1a), which is the outcome that the implementation of control measures is supposed to achieve. In this context, the term "flattening the curve" refers to breaking the exponentially or sub-exponentially increasing velocity curve by reducing acceleration [12]. This is achieved by an effective control measure that reduces the acceleration and thereby creates a positive acceleration peak.…”