Insecticidal malaria nets may stop working after just 12 months in spite of being intended to work for three years, researchers report today.
Writing in the latest edition of BMJ Global Health, the Belgian-led research team, a collaboration between the Médecins Sans Frontières-Operational Centre Brussels and the Institute of Tropical Medicine (ITM), Antwerp, into malaria outbreaks in Burundi Highlands, said it was important to understand why this happened.
The nets are an essential tool in the prevention of malaria cases in Africa and are estimated to have contributed to a worldwide fall in malaria prevalence between 2000 and 2015, averting more than 600 million clinical cases since 2000.
Although the serviceable lifespan of these nets varies, depending on net type and how they are used, the World Health Organization (WHO) recommends they are replaced every three years.
Since 2014, there have been campaigns of these nets in Burundi, East Africa, to distribute the nets, with the aim of universal access.
To establish how effective the nets have been, the researchers drew on routinely collected data on malaria cases between 2011 and 2019 from the National Health Information System in Burundi, focusing on 24 health districts.
During the study period, the government rolled out mass distribution of long-lasting insecticidal malaria nets in June 2014, September 2017, and at the end of 2019, with the aim of providing one bed net for two people in line with WHO standards.
The analysis focused on the first two mass distributions and it showed that malaria incidence rose between 2011 and 2019. It was seasonal, coinciding with an overall average night temperature close to 16°C, and varied according to the altitude of a district.
The data indicated that long-lasting insecticidal nets reduced new cases of malaria in the short term, falling rapidly and sharply during the first year after mass distribution of the nets in 2014 and 2017 in Burundi.
But in the following second and third years, malaria cases started to rise again to levels higher than before mass distribution efforts.
This, say the researchers, suggests the nets lose their effectiveness after one year.
They write: “This study highlights that [long-lasting insecticidal nets] reduced malaria incidence in the first year after a mass distribution campaign in the context of Burundi, but the duration of functional effectiveness seemed to be much shorter than three years that [these] nets should be biologically effective.”
While there could be many reasons for the seemingly rapid loss of effectiveness, they add: “[These nets have] the potential of being an effective vector control intervention in Burundi if the reasons for the fast loss of the impact are understood and can be tackled.”
The authors say this is an observational study, so cannot establish cause, and they acknowledge that diagnosis relied on the availability of rapid diagnostic tests and potential shortages might have affected case reporting. Information on severe disease and age group wasn’t available either.
But they conclude: “Our results highlight the importance of continued epidemiological monitoring of malaria and the utility of routinely collected data to evaluate the temporal and spatial trends of malaria across the country to improve resource allocation and malaria control efforts.”
Van Bortel W, Mariën J, Jacobs BKM et al. Long-lasting insecticidal nets provide protection against malaria for only a single year in Burundi, an African highland setting with marked malaria seasonality. BMJ Global Health 2 December 2022
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