Malaria control programs need information on long-lasting insecticidal net (LLIN) durability to plan replacement strategies to maintain effective coverage. We assessed two LLIN brands distributed in 2015 in Zimbabwe. We used a prospective, longitudinal cohort study to follow one LLIN in each of 2,000 households, with assessments at 6, 18, 24 and 36 months following distribution. We evaluated net fabric integrity and assessed randomly selected LLINs for bio-efficacy and chemical content. The proportion of surviving LLINs was 97% at month 6, 81% at month 18, 75% at month 24, and 64% at month 36. Though decreasing with time, overall survivorship remained above the action threshold of 50% at month 36 for both brands. By contrast, we noted a marked difference between brands in the bioassay and chemical content assessments, with DawaPlus 2.0 showing a greater loss of effectiveness and earlier reductions in chemical content than DuraNet. Re-assessment of the distribution-replacement cycle in Zimbabwe should consider these results, and routine malaria SBC messaging should encourage proper net handling, care and consistent use.

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