The Immunity Paradox of Bed Nets: Why Reducing Exposure Can Still Strengthen Malaria Control

Insecticide-treated bed nets (ITNs) are central to malaria control. They serve as physical barriers and chemical agents that deter and kill mosquitoes, thereby reducing transmission; however, this form of protection reshapes the immunology of malaria by reducing exposure to Plasmodium parasites and weakening the development of naturally acquired immunity. Against this background, the present study develops a modeling framework to investigate how this tension between protection and immunity alters malaria dynamics once vaccination is introduced as a complementary control strategy and the optimum combination of ITN and vaccine coverage required for malaria control. Unlike standard models that use a fixed proportional reduction in transmission, this study models ITN coverage and efficacy as coupled, time-dependent processes and immunity driven by exposure to infection and vaccination. Rigorous analysis of the model identifies existence conditions for equilibria and shows that malaria can be contained through the synergistic interaction of vaccination, vector control, and immunity-mediated host dynamics. Parameter values of the model are estimated by fitting the model to confirmed malaria case data and the estimated baseline reproduction number using these parameter values is 1.41 (95% confidence interval: 1.34-1.48), confirming sustained transmission. Simulations of the model show that, although ITNs reduce immunity acquisition, their net effect is to reduce infections and improve recovery and survival. Hence, population-level benefits of ITNs outweigh their immunity-reducing effects (particularly when combined with vaccination), leading to a reduced malaria burden. Comprehensive sensitivity analysis indicates that malaria burden is driven mostly by mosquito biting intensity, population capacity, and transmission probabilities; while mosquito mortality, effective treatment, ITN performance, and vaccine efficacy cause the most significant reductions. Additionally, malaria is uncontrollable with universal ITN use and vaccination at baseline efficacy. While individual interventions can achieve control under low transmission, neither 100% ITN coverage nor 100% vaccine coverage can achieve control under moderate-to-high transmission. However, a strong synergy between ITNs and vaccination allows combinations of high efficacy to achieve containment at realistic coverage levels, suggesting that integrated malaria control involving effective vector control, vaccination, and prompt treatment is needed.