“…Recently, various models have been created to study the spread of the COVID-19 virus, its mutations, effect of lockdown, and other precautionary measures (see, e.g., Refs. [15] , [16] , [17] , [18] , [19] , [20] , [21] , [22] , [23] , [24] , [25] , [26] , [27] , [28] , [29] , [30] , [31] ).…”