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.