Bhatt et al. (2015)4 studied the decline of cases of malaria in Africa between 2000 and 2015. They found that the single most important contributor to the decli

Bhatt et al. (2015)4 studied the decline of cases of malaria in Africa between 2000 and 2015. They found that the single most important contributor to the decline were insecticide-treated bed nets. According to their findings bed nets were responsible for the aversion of 68% of the 663 million averted cases in Africa between 2000 and 2015. These are 451 million averted cases. Excerpt taken from https://ourworldindata.org/malaria#bed-nets https://ourworldindata.org/malaria#bed-nets . Furthermore only 30% of the population is sleeping under a bed net already in sub-Saharan Africa as mentioned bit further down in the same article. So there's still room for improvements.