Time-variant strategies for optimizing the performance of non-pharmaceutical interventions (NPIs) in protecting lives and livelihoods during the COVID-19 pandemic

Wei Aun Yap; Dhesi Baha Raja

Smooth, submaximal lockdowns. E-series simulation results demonstrate critical tipping point dynamics and include the best performing scenarios (see Figure 7 Scenario E3 or E4, depending on epidemiological outcome of interest) among all scenarios simulated. For NPIs which are implemented strongly, under the parameter estimates used for this hypothetical population, these would represent lockdowns with an intensity of 80% to 100% (see Figure 7 Scenario E2), the NPI suppresses the outbreak during the intervention period but to an extent that prevents the population from attaining herd immunity. Hence, when lifted, the outbreak peaks rapidly. Weak lockdowns with an intensity of 50% or below do not suppress the outbreak and permit a peak even during the period of lockdown. An unstable equilibrium (E3), exists where the right amount of suppression can flatten out the prevalence curve very well over several months. At the end of the intervention, the right balance of immunity within the community and remaining infections fester at a low intensity for a few months more before dissipating without any further NPIs. Importantly, this 'sweet spot' is only relevant for the parameter estimates used, the population characteristics, the stage of the outbreak at which the lockdown was started and the duration of this simulated partial lockdown (168 days from Day 14). The scenario conditions for E3 are not a general rule-of-thumb which can be applied to other populations. Scenario E5 is an important comparator against D-series scenarios as the reduction in 'acts' is the same as pulsatile scenarios with a 50% duty cycle (i.e., D1e to D6). Peak prevalence and incidence for Scenario E5 are lower than for any of these D-series comparators.