Mapping the global prevalence, incidence, and mortality of Plasmodium falciparum and Plasmodium vivax malaria, 2000-22: a spatial and temporal modelling study

Abstract

Background: Malaria remains a leading cause of illness and death globally, with countries in sub-Saharan Africa bearing a disproportionate burden. Global high-resolution maps of malaria prevalence, incidence, and mortality are crucial for tracking spatially heterogeneous progress against the disease and to inform strategic malaria control efforts. We present the latest such maps, the first since 2019, which cover the years 2000-22. The maps are accompanied by administrative-level summaries and include estimated COVID-19 pandemic-related impacts on malaria burden.

Methods: We initially modelled prevalence of Plasmodium falciparum malaria infection in children aged 2-10 years in high-burden African countries using a geostatistical modelling framework. The model was trained on a large database of spatiotemporal observations of community infection prevalence; environmental and anthropogenic covariates; and modelled intervention coverages for insecticide-treated bednets, indoor residual spraying, and effective treatment with an antimalarial drug. We developed an additional model to incorporate disruptions to malaria case management caused by the COVID-19 pandemic. The resulting high-resolution maps of infection prevalence from 2000 to 2022 were subsequently translated to estimates of case incidence and malaria mortality. For other malaria-endemic countries and for Plasmodium vivax estimates, we used routine surveillance data to model annual case incidence at administrative levels. We then converted these estimates to infection prevalence and malaria mortality, and spatially disaggregated administrative-level results to produce high-resolution maps. Lastly, we combined the modelled outputs to produce global maps and summarised tables that are suitable for assessing changing malaria burden from subnational to global scales.

Findings: We found an ongoing plateau in rates of malaria infection prevalence and case incidence within sub-Saharan Africa, with consistent year-on-year improvements not evident since 2015. Due to the concentration of malaria burden in sub-Saharan Africa and the region's rapid population growth relative to other endemic regions, we estimate that 2022 had 234·8 (95% uncertainty interval 179·2-299·0) million clinical cases of P falciparum malaria, the most since 2004. Despite these findings, deaths from malaria continued to decline in sub-Saharan Africa and consequently globally after 2015, except for the COVID-19-impacted years of 2020-22. Similarly, progress in reducing P falciparum and P vivax morbidity outside Africa continued despite stalled progress globally. However, a major malaria outbreak in Pakistan following intense flooding in 2022 resulted in a reversal in this improving trend and contributed heavily to the global total of 12·4 (10·7-14·8) million clinical cases of P vivax malaria. Within Africa, we found that the plateau in infection prevalence occurred earlier in more densely populated areas, whereas more sparsely populated regions have continued a trajectory of modest improvement.

Interpretation: The unprecedented investment in malaria control since the early 2000s has averted an enormous amount of malaria burden. However, case incidence rates in Africa have flattened, and with a rapidly growing population at risk, the number of P falciparum cases in Africa, and thus globally, is now comparable to levels before the surge of investment. Outside Africa progress against malaria morbidity continued after 2015, but a resurgence of P vivax cases in 2022 underscores the fragility of progress against malaria in the face of climatic shocks. COVID-19-related disruptions led to increased malaria cases and deaths, but the impact was less severe than feared, in part because endemic countries continued to prioritise malaria control during the pandemic. Nevertheless, improved tools and strategies remain urgently needed to regain momentum against this disease.

Funding: Bill & Melinda Gates Foundation and Australian National Health and Medical Research Council.

Figure 1

Plasmodium falciparum burden maps for 2022, showing all-age clinical incidence rate (top), infection prevalence in 2–10-year-olds (middle), and all-age mortality rate (bottom) PfPR_2–10= P falciparum parasite rate for 2–10-year-olds.

Figure 2

Plasmodium vivax burden maps for 2022, showing all-age clinical incidence rate (top) and infection prevalence in 1–99-year-olds (bottom) PvPR_1–99=P vivax parasite rate for 1–99-year-olds.

Figure 3

Estimates of global malaria burden from 2000 to 2022 with 95% uncertainty intervals (A) P falciparum clinical incidence rate (new cases per 1000 people per year). (B) P falciparum clinical incidence count (new cases per year, millions). (C) P vivax clinical incidence rate (new cases per 1000 people per year). (D) P vivax clinical incidence count (new cases per year, millions). (E) P falciparum mortality rate (deaths per 100 000 people per year). (F) P falciparum mortality count (deaths per year, thousands). The light blue line shows estimates that include the effect of disruptions to effective treatment coverage which arose due to the COVID-19 pandemic, while the purple line represents a counterfactual scenario of malaria burden in the absence of disruptions to effective treatment coverage. No COVID-19 counterfactual line is shown for P vivax because the COVID-19 adjustments were only done in sub-Saharan Africa where the burden of P vivax is poorly understood. Shaded areas show 95% uncertainty intervals.

Figure 4

Maps of annualised Plasmodium falciparum case incidence changes in Africa between 2005 and 2015 (top) and 2015 and 2020 (bottom) Displayed values were calculated as the change in population-weighted case incidence rate (ie, new cases per 1000 in the end year minus new cases per 1000 in the start year) and annualised by dividing this difference in case incidence rate by the number of years in the period.

Figure 5

PfPR summarised at the level of the largest subnational administrative unit (eg, state) per population density quintiles for the years 2005–20 among the highest burden countries in sub-Saharan Africa, which represent 70% and 74% of the global malaria burden in 2005 and 2020, respectively Boxplots for each time period represent the distribution of population-weighted mean PfPR across all administrative units belonging to each country's population density stratum (eg, the lowest population density quintiles from each country are combined to make the Q1 estimates). The horizontal line within each box is the median and the whiskers are the data values lying within threshold values (quartile 1 – 1·5 × IQR and quartile 3 + 1·5 × IQR); the black dots represent outliers. PfPR=Plasmodium falciparum parasite rate.