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Optimised lockdown strategies for South Africa to curb the spread of COVID-19
Dr Laurentz Olivier Stefan Botha Prof Ian Craig
During the COVID-19 pandemic, many governments around the world implemented tiered lockdown strategies with varying degrees of stringency. Lockdown levels are typically increased when the disease spreads, and reduced when it abates. Researchers in the Department of Electrical, Electronic and Computer Engineering have developed an epidemiological model to determine the most optimal lockdown strategy to curb the spread of the pandemic.
The South African government formulated five lockdown levels with additional allowances in terms of permitted activities for each level to systematically restore economic activity. The model that was developed to determine the epidemiological impact of the lockdown levels imposed used data for the period 23 March to 16 August 2020. The model was adapted with varying values for the spread rate under varying lockdown levels. Finally, a hybrid model predictive control was implemented to determine the optimal lockdown level over time for different policy scenarios: a “flattening the curve” scenario and a “balancing lives and livelihoods” scenario.
THE EPIDEMIOLOGICAL IMPACT OF THE LOCKDOWN LEVELS
From an epidemiological point of view, the early strict lockdown measures imposed by the President of South Africa were successful, but great harm was done to an economy that was already weak before the COVID-19 pandemic started. As a result, significant pressure was applied to relax the lockdown measures, even though the number of infectious individuals was still growing exponentially.
Under the scenario where “flattening the curve” was the goal, the healthcare capacity, expressed in terms of the number of beds available in hospitals’ intensive care units (ICUs), was largely respected, but the lockdown would be long and severe. The detrimental cumulative economic impact of such a long and severe lockdown would be very high.
In terms of the other scenario, which introduced a policy known as “balancing lives and livelihoods”, increased economic activity was permitted by reducing the lockdown levels earlier. This would have the effect of violating the imposed limit of beds in hospitals’ ICUs, but more livelihoods would be saved, and poverty could be reduced.
A final parameter to be considered was that of the population’s compliance with lockdown regulations, which was noted to be reducing the longer a particular lockdown level continued. To curb waning compliance, the lockdown level was increased in the model and extended to the point where the economic loss would be too great and lockdown would be ended rather abruptly.
MODELLING THE DIFFERENT SCENARIOS
The simulation of the “flattening the curve” policy scenario revealed that implementing lockdown at the correct time and at the correct level would allow the active number of confirmed infectious cases to hardly violate the capacity limit of hospitals’ ICUs. The lockdown was implemented relatively early (37 days after the start of the simulation on 18 April 2020) and lasted for 77 days. In terms of the modelling exercise, this scenario would likely have devastating effects for the economy.
The simulation of the “balancing lives and livelihoods” policy scenario showed the implementation of lockdown up to Level 5 to try and curb the spread of the virus, albeit somewhat later than in the “flattening the curve” scenario to alleviate some of the economic impacts of the lockdown. After a couple of weeks on Level 5, the cumulative economic impact was shown to increase to the extent that the level could be reduced, despite the capacity of hospitals’ ICUs being exceeded, in an attempt to curb economic losses. This policy balances lives and livelihoods by delaying the start of Level 5 lockdown by a week and reducing the total time on this level. The advantage of this policy was that the peak in the maximum number of cases could be delayed, as opposed to having no policy in place at all. In addition to winning time, this scenario provided an estimate of the additional number of COVID-19-specific ICU beds required. This implied that if the economic impact of each level of lockdown could be quantified beforehand, temporary ICU facilities could be procured to the point where lockdown might be eased earlier to limit the cumulative economic impact, while the ICU limit could still be respected. However, this scenario needed to be considered against the population’s compliance with the lockdown regulations, which appeared to wane over time. After an initial decrease, the level of compliance in the model was set to increase each time the lockdown level was reduced. This is because there are fewer regulations on lower levels, and the level of compliance with those regulations will likely be higher initially. After the initial surge, compliance was predicted to again reduce in a linear fashion, increasing the spread of the virus. The effect of non-compliance is seen in the higher number of confirmed infectious cases. To curb waning compliance, the lockdown level would be increased and extended to the point where the economic loss would be too great and lockdown would be ended rather abruptly.
