where
S be the number of susceptible human,
E be the number of infectious human which in the
incubation period (exposed human population),
I be the number of infectious human,
R be the number of recovered human who are totally
immune to that strain ,
C be the number of recovered human who are partially
immune to that strain classes.
N is the total of human population,
n B is the birth rate of human population,
μ is the natural death rate of human population,
2 β is the transmission rate which the susceptible human
population become to exposed human,
φ is the transmission rate which the exposed human
population become to infectious human,
α is the transmission rate which the infectious human
population become to the recovered human who are totally
immune to that strain