Note: I am not a malaria expert. This is my best-faith attempt at answering a question that was bothering me, but this field is a large and complex field, and I’ve almost certainly misunderstood something somewhere along the way.

Summary

While the world made incredible progress in reducing malaria cases from 2000 to 2015, the past 10 years have seen malaria cases stop declining and start rising. I investigated potential reasons behind this increase through reading the existing literature and looking at publicly available data, and I identified three key factors explaining the rise:

Population Growth: Africa's population has increased by approximately 75% since 2000. This alone explains most of the increase in absolute case numbers, while cases per capita have remained relatively flat since 2015.
Stagnant Funding: After rapid growth starting in 2000, funding for malaria prevention plateaued around 2010.
Insecticide Resistance: Mosquitoes have become increasingly resistant to the insecticides used in bednets over the past 20 years. This has made older models of bednets less effective, although they still have some effect. Newer models of bednets developed in response to insecticide resistance are more effective but still not widely deployed.

I very crudely estimate that without any of these factors, there would be 55% fewer malaria cases in the world than what we see today. I think all three of these factors are roughly equally important in explaining the difference.

Alternative explanations like removal of PFAS, climate change, or invasive mosquito species don't appear to be major contributors.

Overall this investigation made me more convinced that bednets are an effective global health intervention.

Introduction

In 2015, malaria rates were down, and EAs were celebrating. Giving What We Can posted this incredible gif showing the decrease in malaria cases across Africa since 2000:

Giving What We Can said that

The reduction in malaria has been caused — in large part — by people sleeping under bednets…Long lasting insecticide-treated bednets are a powerful weapon against malaria, not only because they’re a physical barrier between mosquitoes and sleeping children — the insecticide coating kills mosquitoes, so they don’t infect other members of the family (and the village) who don’t have mosquito nets…
In other words, this paper tells us about the

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