Figure 4.

Time histories of the perspective test: August 2021-May 2022. No new COVID-19 variants. The basic reproduction number is kept equal to ${\mathcal{R}}_0=7$ (Delta Variant). The purple line named sihrd-driv vd800 represents our SIHRD-V model-driven results with a vaccination immunity decay time constant of 800 days. We also include the SIHRD-V model-driven results with a vaccination immunity decay time constant of 300 days (the green dashed line named sihrd-driv vd300), and of 1200 days (the orange dotted line named sihrd-driv vd1200). The black line represents the model-free intervention policy, i.e. without any restrictions adjustment. The black dashed line represents the chosen time-varying threshold for the hospitalised population. The hospitalised population remains below the maximum accepted time-varying threshold with the use of our intervention strategy.