Optimizing Indoor Residual Spraying

Two complementary studies examined whether the long-standing 80% coverage target for indoor residual spraying (IRS) is the right benchmark. A retrospective analysis published in PNAS used four years of high-resolution programmatic data to estimate a dose-response curve, finding that community protection thresholds were reached at coverage levels of 30% to 50%, far lower than assumed. Building on this, a prospective non-inferiority trial published in the WHO Bulletin tested 50% coverage against 80% in a cluster-randomized design and found no evidence that the lower target was inferior.

Together, these studies provide both observational and experimental evidence that optimized IRS coverage can increase the overall reach of this intervention to the at-risk population while freeing up resources for complementary interventions The BIMEP has since redefined its integrated vector control strategy by reinvesting in larval source management.

Strengthening Surveillance

Standard rapid diagnostic tests miss a significant number of infections. Another study integrated molecular monitoring into routine malaria indicator surveys and found a high proportion of low-density infections, particularly in urban communities. These infections evade detection but sustain transmission; an invisible reservoir that complicates elimination efforts. The findings underscore the need for more sensitive diagnostic approaches as programs move toward elimination.

The Challenge of Importation

Even with strong local interventions, malaria is regularly reintroduced to Bioko Island, Equatorial Guinea, from the mainland and neighboring countries. Genetic analysis of parasite populations confirmed that importation is a persistent driver of transmission on the island. This research reinforces that elimination on Bioko Island cannot succeed in isolation and requires regional coordination and targeted interventions for mobile populations.

Monitoring Drug Quality

Effective treatment depends on quality-assured antimalarials reaching patients. A follow-up study on antimalarial drug quality in Equatorial Guinea identified ongoing gaps in the drug supply chain. These findings provide actionable data to support national efforts to strengthen pharmaceutical regulation and ensure that patients receive medicines that work.

Reaching Vulnerable Populations

Pregnant women face elevated risks from malaria, yet many are missed by routine health services. The BIMEP explored whether IRS household visits could serve as a platform for maternal health outreach. By engaging with women during spray campaigns, the team was able to improve awareness of bed nets and intermittent preventive treatment in pregnancy (IPTp). This integrated approach demonstrates how vector control activities can address broader health needs.

Evidence into Action

The value of operational research is in its translation to practice. In 2025, the BIMEP's annual malaria indicator survey recorded 7.2% prevalence (all ages), the lowest in over a decade. This milestone suggests that the adaptive, evidence-driven approach is working. As the BIMEP enters a new phase with national expansion and partnerships on next-generation tools, including gene drive technologies and malaria vaccines, the foundation remains the same: generate evidence, refine strategy, and deliver impact.

2025 BIMEP Publications:

• Published in PNAS: Reconsidering indoor residual spraying coverage targets: A retrospective analysis of high-resolution programmatic malaria control data (learn more).
• Published in Bulletin of the WHO: Testing indoor residual spraying coverage targets for malaria control, Bioko, Equatorial Guinea (learn more).
• Published in Malaria Journal: Integrating local malaria molecular monitoring into regular malaria indicator surveys on Bioko Island: high association between urban communities and low-density infections (learn more).
• Published in PLOS Global Public Health: Regular Plasmodium falciparum importation onto Bioko Island, Equatorial Guinea, hampers malaria elimination from the island (learn more).
• Published in BMJ Global Health: Assessing the quality of antimalarial drugs in Equatorial Guinea: a follow-up study (learn more).
• Published in BMC Pregnancy and Childbirth: Indoor residual spraying household visits as a platform for engaging pregnant women in malaria prevention on Bioko Island, Equatorial Guinea (learn more).
• Published in The American Journal of Tropical Medicine and Hygiene: Assessment of Health Status and Creation of a Registry of Potential Research Participants Age 1.5 to 50 Years on Bioko Island, Equatorial Guinea (learn more).

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