BACKGROUND: The evaluation of new long-lasting insecticidal bed nets (LLINs) is coordinated by the WHO Pesticide Evaluation Scheme (WHOPES). In 2007, Netprotect® was granted WHOPES interim recommendation after Phase I and II evaluations. Present study evaluates Netprotect in a Phase III trial in rural Cambodia.
METHODS: A randomized, prospective longitudinal study design was used to assess the performance of Netprotect over a period of three years, using conventionally-treated nets and a WHOPES recommended LLIN (PermaNet 2.0) as positive controls. The primary outcomes were the physical integrity, insecticide content and cone bioassay performance using.
RESULTS: The baseline deltamethrin concentration of 43% of Netprotect nets were below the tolerance limit while 27% of PermaNet 2.0 nets were above the target dose limits. By 36 months Netprotect retained 35% while PermaNet 2.0 retained 49% of baseline insecticide dose. Moreover the proportion of the inactive deltamethrin R-alpha isomer in the Netprotect nets was 33% at the baseline and increased to 69% after three years while it was low and almost constant for PermaNet® 2.0 (3-7%). Only 71% of Netprotect met the WHO criteria for bio-efficacy after three years while at least 80% is required. Moreover Netprotect nets failed for the WHOPES criteria after 12 and 24 months. The reference LLIN met the WHOPES criteria throughout the study. Over the entire three years the reference LLIN did obtain significant higher mosquito mortality than Netprotect. The physical integrity was based on the proportionate hole index and after three years, 25% of Netprotect and 30% of PermaNet 2.0 were in a mediocre or poor state.
CONCLUSION: Netprotect did not meet the minimum WHO criteria for bio-efficacy after 12, 24 and 36 months. The use of a reference LLIN as positive control was helpful for data interpretation. However, for future three-year studies, it is essential that before initiating any study nets should be checked for their specifications and this for both the candidate LLIN as well as for the reference LLIN. Moreover, to improve the accuracy of the success rate of the candidate LLIN more nets should be tested for their bio-efficacy at the end of the trial.