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Environmental factor, barrier 4 of 9

Infectious disease environment

Infectious disease harms health and schooling.

Evidence

  • Malaria. WHO's World Malaria Report 2025 estimated 282 million cases and 610,000 deaths in 2024, up from a revised 273 million cases in 2023. About 95% of deaths occurred in the WHO African Region, mostly among children under 5. Because most victims are young children, malaria removes potential future contributors, including possible pioneers, before any ability can develop.
  • Parasites and schooling. The Rockefeller Sanitary Commission found 40% of school-aged children in the American South had hookworm. Bleakley (2007) found areas with higher infection saw larger gains in enrollment, attendance, literacy, and later income after treatment. An independent replication (Roodman, 2018) questioned whether these benefits are robust.

Why it matters: A disease-heavy environment can look like a lack of effort or ability. Remove the disease and the "deficit" often shrinks.

Proposed and experimental methods

Methods that are proposed, under trial, approved in some places, or tried and then failed. Each shows a stage label and an evidence rating. A stage label shows how far a method has progressed, not whether it works. The stage labels are explained on the environmental factor page.

  • Dual active ingredient bed nets (Approved but not scaled, A). Nets that add chlorfenapyr, an insecticide with a different mode of action, to a pyrethroid, because mosquitoes now resist pyrethroids. In a four-arm cluster randomized trial in Tanzania, malaria infection at 24 months was 25.6% with chlorfenapyr nets versus 45.8% with standard nets (adjusted odds ratio 0.45) (Mosha et al., 2022), and in Benin malaria incidence was 0.56 versus 1.03 cases per child-year (hazard ratio 0.54) (Accrombessi et al., 2023). WHO issued a strong recommendation for these nets in 2023 (WHO, 2023). Net use fell to 41% to 61% by 24 months, and the Tanzania authors call for resistance management before scale-up.
  • Malaria vaccines R21 and RTS,S (Approved but not scaled, B). In a phase 3 trial of 4,878 African children, R21/Matrix-M had 75% efficacy against clinical malaria over 12 months at seasonal sites and 68% at year-round sites (Datoo et al., 2024). When RTS,S was introduced through routine immunization in Ghana, Kenya, and Malawi with randomized timing across 158 areas, eligible children had 32% fewer hospital admissions with severe malaria and 9% lower all-cause mortality, and the earlier safety signals did not appear (Asante et al., 2024). Third-dose coverage was 62% to 66%.
  • Wolbachia-infected mosquitoes (Approved but not scaled, contested, B). Releasing Aedes mosquitoes carrying the Wolbachia bacterium, which blocks dengue transmission. In a cluster randomized trial in Yogyakarta, Indonesia, dengue was 77.1% lower and dengue hospitalization 86.2% lower in release areas (Utarini et al., 2021). In Campo Grande, Brazil, stable establishment was associated with 63.2% less dengue (de Morais Batista et al., 2025), but in Rio de Janeiro only 32% of local mosquitoes carried Wolbachia and it failed to recover after insecticide use (Pavan et al., 2025). One review calls for a pause and independent re-evaluation, citing loss of Wolbachia and outbreaks in release zones (Marinotti et al., 2026).
  • Spatial repellents (Large trial, contested, C). Devices that release a repellent, here transfluthrin, into the air of a home. In western Kenya, with high net coverage, they cut first-time malaria infection by 33.4% (Ochomo et al., 2025), but a sister trial in Mali found no effect (protective efficacy -3.10%) in a not yet peer-reviewed report (Sagara et al., 2025).
  • Reversed: Target Malaria in Burkina Faso (Failed or reversed, B). Target Malaria is developing genetically modified mosquitoes, with gene drive as the long-term goal, to suppress malaria vectors. In August 2025 Burkina Faso's authorities ordered all of its activities in the country stopped, days after a small release of non-gene drive modified male mosquitoes, and the project gave no reason in its statement (Target Malaria, 2025).

Sources cited on this page

  1. WHO: Burden of disease from unsafe water, sanitation and hygiene, 2019 update (2023) B Moderate
  2. Bleakley, H. (2007). Disease and development: evidence from hookworm eradication in the American South. Quarterly Journal of Economics, 122(1), 73-117. Oxford Academic C Limited
  3. Roodman, D. (2018). The impacts of hookworm eradication in the American South: a replication study of Bleakley (2007). International Journal for Re-Views in Empirical Economics, 2, 1-45. JCR-Econ B Moderate
  4. Ma, L., Graham, D. J., & Stettler, M. E. J. (2021). Has the ultra low emission zone in London improved air quality? Environmental Research Letters, 16, 124001. link B Moderate
  5. Accrombessi, M., Cook, J., Dangbenon, E., Yovogan, B., Akpovi, H., Sovi, A., et al. (2023). Efficacy of pyriproxyfen-pyrethroid long-lasting insecticidal nets (LLINs) and chlorfenapyr-pyrethroid LLINs compared with pyrethroid-only LLINs for malaria control in Benin: A cluster-randomised, superiority trial. Lancet, 401(10375), 435-446. link A Strong
  6. Asante, K. P., Mathanga, D. P., Milligan, P., Akech, S., Oduro, A., Mwapasa, V., et al. (2024). Feasibility, safety, and impact of the RTS,S/AS01E malaria vaccine when implemented through national immunisation programmes: Evaluation of cluster-randomised introduction of the vaccine in Ghana, Kenya, and Malawi. Lancet, 403(10437), 1660-1670. link B Moderate
  7. Datoo, M. S., Dicko, A., Tinto, H., Ouédraogo, J.-B., Hamaluba, M., Olotu, A., et al. (2024). Safety and efficacy of malaria vaccine candidate R21/Matrix-M in African children: A multicentre, double-blind, randomised, phase 3 trial. Lancet, 403(10426), 533-544. link B Moderate
  8. de Morais Batista, F., Carcamo, P. M., Nelson, E., da Silva Neto, A. B., Tsuha, D. H., Lahdo, V., et al. (2025). The impact of large-scale release of Wolbachia mosquitoes on dengue incidence in Campo Grande, Brazil: An ecological study. Lancet Regional Health: Americas, 54, 101327. link C Limited
  9. Marinotti, O., Paldi, N., & Gorla, D. (2026). Wolbachia releases for dengue control: Why the evidence supports a pause and independent re-evaluation. Infectious Diseases, 58(10), 991-1001. link C Limited
  10. Mosha, J. F., Kulkarni, M. A., Lukole, E., Matowo, N. S., Pitt, C., Messenger, L. A., et al. (2022). Effectiveness and cost-effectiveness against malaria of three types of dual-active-ingredient long-lasting insecticidal nets (LLINs) compared with pyrethroid-only LLINs in Tanzania: A four-arm, cluster-randomised trial. Lancet, 399(10331), 1227-1241. link A Strong
  11. Ochomo, E. O., Gimnig, J. E., Awori, Q., Abong'o, B., Oria, P., Ashitiba, N. K., et al. (2025). Effect of a spatial repellent on malaria incidence in an area of western Kenya characterised by high malaria transmission, insecticide resistance, and universal coverage of insecticide treated nets (part of the AEGIS Consortium): A cluster-randomised, controlled trial. Lancet, 405(10473), 147-156. link B Moderate
  12. Pavan, M. G., Gnonhoue, F. J., Corrêa-Antônio, J., Padilha, K. P., Garcia, G. A., de Oliveira, F., et al. (2025). The long-term persistence of the wMel strain in Rio de Janeiro is threatened by poor integrated vector management and bacterium fitness cost on Aedes aegypti. PLoS Neglected Tropical Diseases, 19(7), e0013372. link C Limited
  13. Sagara, I., Dicko, A., Thera, I., Coulibaly, M., et al. (2025). Effect of a spatial repellent on malaria incidence in Mali: A cluster-randomized, controlled trial [Preprint]. medRxiv. link C Limited
  14. Utarini, A., Indriani, C., Ahmad, R. A., Tantowijoyo, W., Arguni, E., Ansari, M. R., et al. (2021). Efficacy of Wolbachia-infected mosquito deployments for the control of dengue. New England Journal of Medicine, 384(23), 2177-2186. link B Moderate
  15. Roodman, D. (2024). The arrival of fast internet and employment in Africa: Comment (I4R Discussion Paper No. 148). Institute for Replication. link B Moderate
  16. South, E. C., Hohl, B. C., Kondo, M. C., MacDonald, J. M., & Branas, C. C. (2018). Effect of greening vacant land on mental health of community-dwelling adults: A cluster randomized trial. JAMA Network Open, 1(3), e180298. link B Moderate

Every source for this factor is listed on the environmental factor page.