Estimation of the Reproduction Number for COVID-19 Based on Latest Vaccination Results and the Timing for Herd-Immunity: Prospect for 2021

This study examined four countries Israel, United States, United Kingdom, and Serbia and present their possible vaccination trajectories into 2021. We found that populations in all the four countries are relaxing and taking the advantage of the benefit of an increasingly immunized community hence, experiencing a rising phase of Rc(t). The United States is of particular concern, due to its fast rising Rc(t) in comparison to other countries, potentially generating another wave of infection. Due to aggressive vaccination program, continued implementation of restrictive measures, or both, in all countries we analyzed, present a cautiously optimistic outlook at controlling the pandemic toward the latter part of 2021. We also found that despite a significant fraction of the population in selected countries being immunized, no countries other than Israel has its Rc(t) reached its intrinsic R0 value. Based on our proposed methodology for deriving R0, our prediction shows that Israel's indigenous COVID-19 daily R0 is approximately 2.2 based on its latest data.