Impact of mass distribution on insecticide-treated net coverage and usage in three high burden malaria provinces of Papua New Guinea.

BACKGROUND: Papua New Guinea (PNG) completed five nation-wide mass distributions of insecticide-treated nets (ITNs) in the last 15 years. Despite this considerable achievement, malaria cases in PNG are rising. Recent national-level surveys indicate unusually low ITN coverage and usage indicators, raising concerns about the continued effectiveness of this core intervention. Significant knowledge gaps remain around factors impacting ITN effectiveness in PNG, limiting interpretation of the role of ITNs in the context of rising malaria cases. This study assessed how ITN ownership and usage indicators in three of the highest burden provinces changed after the most recent mass distribution in 2024. METHODS: Cross-sectional surveys involving a target of 60 randomly selected households per village were conducted in 12 villages in East Sepik, West Sepik and Madang province and collected data on 5671 individuals belonging to 815 households. The surveys were conducted within 1-4 months before (September-December 2023), and 5-7 months after (May-October 2024) programmatic ITN mass distribution. Data were collected through household questionnaires, visual inspection of all ITNs present in households, and matching of ITNs to individual users. Household-level and person-level indicators of ITN ownership and use were evaluated using generalised linear mixed effects models. RESULTS: Distribution targets were achieved in two provinces but were missed by 38-42% in the third province. Overall, 94.8% of houses owned at least one ITN, before, and 99.4% after distribution (P < 0.001). The mean number of ITNs per person rose from 0.55 to 0.64 (P < 0.001), and universal coverage increased from 60.0% before to 69.9% after distribution (P = 0.002). ITN distribution resulted in 61.1% of new ITNs in use and 55.5% of old ITNs lost to follow-up at the post distribution survey. Distribution increased ITN usage evenly across genders and ages and did not change existing overall age- or gender-related usage and sharing patterns. CONCLUSIONS: ITN ownership and use are high and sustained by 3-yearly distributions in the three provinces. ITN use was primarily driven by availability, with no further increases observed beyond universal coverage. Results also highlight the importance of post-distribution surveillance to confirm that programme targets are achieved.