The results of the present work may also be useful in estimation of the parameter values for ADE and cross immunity. ADE especially is difficult to measure in vivo and must be estimated by other means. Since recent publications have suggested that epidemiological data from Thailand show chaotic outbreaks , and given the certainty of human migration and asymmetry between adjacent regions of the country, it is possible that the actual parameter values for ADE and cross immunity are higher than the ones estimated by studying a single, well-mixed population.