Mosquito Nets Do Prevent Malaria, Longitudinal Study Confirms Mosquito Nets Do Prevent Malaria, Longitudinal Study Confirms

It seems obvious that increased use of mosquito bed nets in sub-Saharan Africa would decrease the incidence of malaria, but a lingering question remained: would controlling malaria in children under 5 years of age shift deaths to older children by delaying functional immunity?  A new report in the New England Journal of Medicine seems to have laid that concern to rest.

Malaria from Plasmodium falciparum infection exacts a significant toll in sub-Saharan Africa. According to the World Health Organization, there were about 228 million cases and 602,000 deaths from malaria in 2020 alone. About 80% of those deaths were in children less than 5 years old. In some areas, as many as up to 5% of children die from malaria by age 5.

Efforts to reduce the burden of malaria have been ongoing for decades. In the 1990s, insecticide-treated nets were shown to reduce illness and deaths from malaria in children.

As a result, the use of bed nets has grown significantly. In 2000, only 5% of households in sub-Saharan Africa had a net in the house. By 2020, that number had risen to 65%. From 2004 to 2019 about 1.9 billion nets were distributed in this region. The nets are estimated to have prevented more than 663 million malaria cases between 2000 and 2015.

As described in the NEJM report, public health researchers conducted a 22-year prospective longitudinal cohort study in rural southern Tanzania following 6706 children born between 1998 and 2000. Initially, home visits were made every 4 months from May 1998 to April 2003. Remarkably, in 2019, they were able to verify the status of fully 89% of those people by reaching out to families and community/village leaders.

Günther Fink, PhD, associate professor of Epidemiology and Household Economics, University of Basel, Switzerland, explained the approach and primary findings to Medscape Medical News. The analysis looked at three main groups—children whose parents said they always slept under treated nets, those who slept protected most of the time, and those who spent less than half the time under bed nets. The hazard ratio for death was 0.57 (95% CI, 0.45-0.72) for the first two groups compared with the least protected. The corresponding hazard ratio between age 5 and adulthood was 0.93 (95% CI, 0.58-1.49).

The findings confirmed what they had suspected. Fink summarized simply, “If you always slept under a net, you did much better than if you never slept under the net. If you slept [under a net] more than half of the time, it was much better than if you slept [under a net] less than half the time.” So the more time children slept under bed nets, the less likely they were to acquire malaria. Fink stressed that the findings showing protective efficacy persisted into adulthood. “It seems just having a healthier early life actually makes you more resilient against other future infections.”

One of the theoretical concerns was that using nets would delay developing functional immunity and that there might be an increase in mortality seen later. This study showed that did not happen.

An accompanying commentary noted that there was some potential that families receiving nets were better off than those that didn’t but concluded that such confounding had been accounted for in other analyses.

Mark Wilson, ScD, professor emeritus of epidemiology, University of Michigan, Ann Arbor, concurred. He told Medscape Medical News that the study was “very well-designed,” and the researchers “did a fantastic job” in tracking patients 20 years later.

“This is astounding!” he added. “It’s very rare to find this amount of follow-up.”

Fink’s conclusion? “Bed nets protect you in the short run, and being protected in the short run is also beneficial in the long run. There is no evidence that protecting kids in early childhood is weakening them in any way. So we should keep doing this.”

Fink and Wilson report no relevant financial relationships.

NEJM 2022;386:428-36. DOI: 10.1056/NEJMoa2112524 Article

Judy Stone, MD, is an infectious disease specialist and author of Resilience: One Family’s Story of Hope and Triumph Over Evil and of Conducting Clinical Research , the essential guide to the topic. You can find her at drjudystone.com or on Twitter @drjudystone .

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