Rt is directly related to the second-order reaction rate constants which reflect the collision frequency of individuals and the energy barriers of the disease infection. Re is related to the quasi-first-order reaction rate constant that has been normalized to the concentration of the susceptible population in the community. The Re value as designed directly correlated with the growth and decline of the daily cases and its magnitude away from 1 reflects the exponential grow or decline rate like the interest rate or payback rate in a mortgage. However, it does not reflect the effect of social regulations as well as Rt, especially in the later stage of the spread. In the later stage, the concentration of the susceptible population has been significantly reduced due to immunity either from recovery or vaccination. Thus, Rt is a more valuable value than Re to trace the pandemic during these spreading stages. The resulting Rt from the SIRV model (Figure ) is consistent with our experience that travel and social activities are almost fully recovered around 2022 new year which brings the Rt value back to near R0 in all the randomly chosen states. Both SIR (Figure ) and SIRV model (Figure ) give the same Re values but SIR model significantly lower estimates the Rt values when vaccination is significant.