Discussion
scabies
SCABIES
In this trial of one versus two doses of ivermectin for scabies control, we did not observe a change in scabies prevalence between baseline and 21 months following MDA in either arm. The upper limit of the 95% confidence interval of the difference between the two study groups comparing baseline to 21 months was greater than 5% so we could not conclude that a single dose was non-inferior. However, there was a clear reduction in scabies severity in both arms, and clinics servicing study villages reported a modest decline in consultations for scabies in contrast to other clinics of the province which reported no change.Our initial plan to conduct follow-up visits at both 12 and 24 months had to be modified when the Solomon Islands Ministry of Health and Medical Service paused health research in 2020 to minimise risks and maximise resources directed at the COVID-19 pandemic response. The 21-month procedures were unchanged from the planned for 12 and 24 months, apart from the remote involvement of the Australia-based study coordinator (SL).The lack of reduction in scabies prevalence following ivermectin-based MDA in either arm was unexpected. In trials conducted in other provinces in Solomon Islands, we have recorded substantial declines attributed to this intervention and similar findings have been reported from studies in Fiji [Other studies in the region have shown significant reduction in scabies prevalence 24 and 36 months after MDA so it is unlikely that the follow up period was too long to capture the impact of MDA [Lower numbers of participants at 21 months, combined with a high proportion of participants in both arms reporting they had not been present during the MDA, indicate substantial movement both in and out of villages. As the study was designed to assess change in scabies prevalence at the village level, rather than the individual level, we were unable to link participant data between baseline and 21 months so relied on participants self-reporting if they had participated at baseline. There is evidence that people can accurately recall whether or not they received MDA up to 12 months after treatment, there is not published information on recall accuracy at longer time intervals [The ivermectin and permethrin that we used for this study were from international suppliers and met appropriate international quality standards including Good Manufacturing Practice (GMP). The study team directly observed participants taking ivermectin. Therefore, it is unlikely that either the quality of the treatments or adherence had any impact on the study outcomes.There are a small number of health clinics that service the area of the study villages. We were unable to differentiate presentations by study arm as each clinic services multiple villages and aggregate consultation data at the clinic level. The small reduction in the proportion of scabies presentations in the 12 months after MDA in the clinics that service study villages compared to those that do not may further support the hypothesis that there was an initial decline in scabies prevalence following MDA, but it was undetectable at 21-months due to the unexpected population movement and the presumed re-introduction and transmission of scabies.While the timing of trial procedures was affected by the COVID-19 pandemic, our procedures remained essentially intact. Beyond our control was the increased population movement which appears to have reduced the effectiveness of the ivermectin-based MDA strategy that has previously worked so well in Solomon Islands and other Pacific Island countries. Despite the challenges of this trial, recent results from a trial in Fiji indicate that single dose ivermectin is highly promising as a more practical means of delivering MDA [