Discussion
malaria, malaria infection
MALARIA
In this CRT assessing the effectiveness of a new class of LLIN over 3 years, children residing in clusters that received PBO-Pyrethroid-LLINs had reduced odds of malaria infection compared to those who received standard LLINs up to 28 months post-intervention when half of the participants were still using the study nets. This effect became weaker and was no longer significant after a further 6 months when usage had dropped and most of the PBO content from the nets was lost. By the 36th month only 4% of the original PBO and half of the permethrin remained in the net [Permethrin content in the PBO-Pyrethroid-LLINs and standard LLINs halved after 36 months, while PBO was reduced by 97% of the initial concentration [In the first two years of our trial, an effect of PBO-Pyrethroid-LLINs on malaria transmission and vector density was observed when concentrations of PBO were reduced to 16% of the initial content. Personal protection against The shorter than expected effective lifespan of PBO-Pyrethroid-LLINs and standard LLINs was also observed in a separate cohort of nets followed annually as part of this study showing that less than 17% of the nets distributed survived up to 3 years as assume. The development of holes in nets was the main driver of decreasing usage [The WHO currently requires CRTs assessing the public health value new classes of LLINs to be conducted over a minimum of two transmissions seasons, while also expecting all classes of LLIN to demonstrate three years of working life. However, without good evidence relating to the longevity of LLINs procurement and distribution agencies are unlikely to change their assumption of a 3 year useful lifespan of nets to a more realistic replacement cycle of the product. NMCPs should therefore conduct routine monitoring and assessments of the impact of ageing of PBO-Pyrethroid-LLIN after their distributions as it will vary depending on brands and settings. The Tanzanian continuous delivery mechanism of LLINs through annual distributions to primary school children and antenatal consultations, rather than mass distribution campaigns, seems more in tune with the PBO-Pyrethroid-LLIN lifespan thereby maintaining good coverage [The absence of effect observed in the IRS group was expected as pirimiphos-methyl does not last on walls of houses for more than 9 months [