Monitoring the durability of the long-lasting insecticidal nets Olyset® and PermaNet® 2.0 in similar use environments in Zanzibar.

BACKGROUND: Malaria transmission in Zanzibar has dramatically reduced in recent years but vector control interventions such as long-lasting insecticidal nets (LLIN) must continue to reach malaria elimination. To achieve this, the Zanzibar Malaria Elimination Programme needs actionable evidence of the durability of the LLIN brands distributed. This study compared physical and insecticidal durability of two LLIN brands: Olyset® and PermaNet© 2.0 in two similar districts on the islands of Unguja and Pemba. METHODS: This was a prospective cohort study of representative samples of households from two districts, recruited at baseline 4 months after the mass campaign. All campaign nets in these households were labelled and followed up over a period of 33 months. Primary outcome was the "proportion of nets surviving in serviceable condition" based on attrition and integrity measures and the median survival in years. The outcome for insecticidal durability was determined by bio-assay from sub-samples of campaign nets. RESULTS: A total of 834 campaign nets (121% of target) from 299 households were included in the study. Definite outcomes could be determined for 86% of the cohort nets in Unguja (PermaNet® 2.0) and 89% in Pemba (Olyset®). After 33 months, physical survival in serviceable condition was 55% in Unguja and 51% in Pemba. Estimated median survival was lower in Pemba at all time points with 2.3-2.7 years compared to 3.1-3.3 yeas in Unguja. Multivariable Cox proportionate hazard models confirmed the difference between brands (p < 0.0001) and identified household net-care attitude (p = 0.007) and folding of hanging nets during the day (p < 0.0001) as significant determinants, in addition to exclusive use of nets by adults (p = 0.03) and use only over a finished bedframe (p = 0.01). Optimal insecticidal effectiveness was 80% or higher for both brands at all time points when both cone bio-assays and tunnel tests were applied. CONCLUSIONS: After 3 years of follow-up, Olyset® LLIN showed significantly lower physical survival compared to PermaNet® 2.0 LLIN even after adjusting for other variables of net-use environment and net handling. This suggests that the differences were driven by the textile characteristics of the LLIN brands.

Sustaining LLIN coverage with continuous distribution: the school net programme in Tanzania.

Most malaria-endemic countries have struggled in the past decade to establish effective national-scale continuous distribution mechanisms for long-lasting insecticidal nets (LLINs). Since the implementation of the Tanzania National Voucher Scheme in 2004 and mass-distribution campaigns in 2009-2011 and 2015-2016, Tanzania has been committed to finding new and innovative ways of achieving and maintaining universal bed net coverage. Planning for the School Net Programme (SNP) began in 2011 and in 2013, the country piloted a SNP in three regions. Nets were distributed annually to children attending schools in selected primary and secondary grades. Intra-family re-distribution was assumed, and hence the family as a whole, rather than just the children themselves, were the targeted beneficiaries. The programme has since expanded to 14 regions and has seen six rounds of annual distribution. In its fifth year, 3 million nets were distributed at a cost of USD 3.64 per net and USD 0.60 per person-year of protection (including the net). ITN access and use were maintained at a high level (~ 50-75%) over the first 4 years of distribution within selected evaluation areas, even in the absence of a mass distribution event. Net distribution through primary schools has proven to be a feasible and effective strategy for maintaining consistently high coverage in Tanzania.