Abstract-We discuss an epidemic model for dengue fever infection by considering the simultaneous spread of two serotypes throughout a shared non-naive host population and analyze the dynamics of the spreading for each serotype. The susceptible population is divided into two different susceptible classes: a naive population for those individuals that have never been exposed to the virus and a cross-imune population whose individuals have been exposed to one of the serotypes becoming immune to it but susceptible to its heterelogous. When the cross-immune populations are different an asymmetry in the susceptible host population is introduced and the dynamics of strains spreading is investigated as a function of this asymmetry. We show that the asymmetry in initial condition expressed by differences on the size of cross-imune population induces a feedback mechanism which produces an alternate pattern in epidemics with different dominant serotypes. We found that if the susceptible populations are symmetric both serotypes coexist during the epidemics but when the asymmetry becomes large two epidemics could be distinguished with a predominant serotypes in each one.