Spread of refractoriness in the absence of a transposon as a genetic drive mechanism, and its effect on the prevalence of malaria in the human population at equilibrium under the assumption of a conditional cost of refractoriness that is induced by the response to parasite infection. The parameters used to simulate the equations were: biting rate a = 0.5 day-1, mortality μ = 0.1 day-1, virulence = 0.1 and dominance h = 0.9. In panels (a) and (b) the efficacy of refractoriness was held at s = 1, and the cost of refractoriness and the initial intensity of transmission (i.e. before the spread of refractoriness) were varied. In panels (c) and (d) the cost of refractoriness was held at c = 0.05, and the efficacy of refractoriness and the initial intensity of transmission were varied.