“…Thus, using a fractional derivative to build up a COVID-19 model may address gaps between data and the existing knowledge on the COVID-19 transmission process. However, in all of the existing fractional order models on COVID-19 [25] , [26] , [27] , [28] , [82] , [83] , [84] , [85] , instead of taking fractional derivatives in the force of infection in disease transmission, authors used fractional derivatives only in the population (left-hand side of the system replacing ordinary derivatives with some fractional order derivative), which in general a Markovian process [20] , [21] , [35] , [36] , [38] . Consequently, these models may not be appropriate to study the power law/memory effect in the transmission process of COVID-19.…”