Safety and efficacy of repeat ivermectin mass drug administrations for malaria control (RIMDAMAL II): a phase 3, double-blind, placebo-controlled, cluster-randomised, parallel-group trial.

BACKGROUND

The success of crucial vector control efforts in Africa (eg, long-lasting insecticide-treated nets [ITNs] and indoor residual spraying) are threatened by widespread insecticide resistance and insufficient effect on outdoor mosquito biting. Studies have shown that ivermectin, used for the treatment of parasitic diseases, can kill malaria vectors that feed on the blood of treated people and thus might be an effective complementary vector control tool if administered widely to communities in malaria endemic regions. We aimed to test the safety of repeated, high-dose ivermectin mass drug administration (MDA) and its efficacy for reducing malaria incidence among children when integrated with seasonal malaria chemoprevention (SMC) delivery.

METHODS

We conducted a phase 3, double-blind, placebo-controlled, cluster-randomised, parallel-group trial in southwest Burkina Faso over two consecutive rainy seasons (2019-20). 14 villages or village sectors (clusters) were randomly assigned (1:1) to ivermectin or placebo MDA by random draw, and study-eligible participants (those who regularly lived in the cluster and provided written informed consent) from all households were enrolled in July, 2019 and July, 2020. Participants were eligible for MDA if they were 90 cm in height or taller and not excluded for other safety reasons (eg, pregnancy or taking SMC drugs). There were no age restrictions for participants. Each rainy season (July to October), eligible participants from the intervention group clusters received monthly high-dose oral ivermectin MDA (three daily doses, approximately 300 μg/kg dosed by height bands) and those from the control group received monthly oral placebo MDA for up to eight treatment rounds. MDA was performed by study staff alongside community health worker administration of monthly SMC to children aged 3-59 months in both groups. All participants and study personnel, apart from the pharmacist, were masked to group assignment. The primary outcome was weekly malaria incidence in children aged 10 years and younger, as assessed by weekly active case detection until week 16 of year 2, by intention to treat. Adverse events were monitored in all MDA participants through active and passive surveillance. Blood was sampled for secondary parasitological outcomes, including analysis of parasite species distribution among malaria cases. Mosquitoes were sampled from pre-selected households in three clusters per group for secondary entomological outcomes, including analysis of blood-fed mosquito survivorship, mosquito biting rates, and entomological inoculation rates. Changes in haemoglobin pre-intervention and post-intervention in children aged 10 years and younger were assessed in 2020. The trial is registered with ClinicalTrials.gov (NCT03967054) and the Pan African Clinical Trials Registry (PACT201907479787308) and is completed.

FINDINGS

The study took place from July 13, 2019, to Nov 8, 2020, with seven villages assigned to the control group and seven to the intervention group. Participants were enrolled from households in both groups in July, 2019, and July, 2020. In the intervention group, 1928 participants in 2019 and 2163 participants in 2020 were followed up, and 703 children in 2019 and 686 children in 2020 were analysed. In the control group, 1604 participants in 2019 and 1921 participants in 2020 were followed up, and 605 children in 2019 and 641 children in 2020 were analysed. MDA coverage (receiving ≥1 dose) in the enrolled population (including those who were ineligible) varied over the intervention period (68-74%), with 86-95% of participants who were eligible receiving ivermectin or placebo over the study period. 288 (47·2%) of 610 children in the control group and 312 (44·2%) of 706 children in the ivermectin group received SMC, and all clusters received new dual-chemistry Interceptor G2 ITNs containing chlorfenapyr and α-cypermethrin by government authorities in October, 2019. The average estimated weekly malaria incidence rate per 100 person-weeks among children in the intervention group was 1·78 (95% CI 1·24-2·53) and 1·84 (1·29-2·64) in the control group, and the incidence rate ratio was 0·96 (95% CI 0·58-1·59; p=0·8723). The risk of adverse events among eligible participants in the intervention group was lower than in the control group (risk ratio 0·63, 95% CI 0·46-0·87; p=0·0049). The distribution of Plasmodium spp detected in children with clinical malaria was unexpectedly diverse with non-Plasmodium falciparum species detected in 56 (11%) of 505 symptomatic children; however, species distribution did not differ between groups (p=0·15). Blood-fed Anopheles gambiae species complex mosquitoes captured in intervention group clusters the week after MDA in 2019 had decreased survival relative to those captured from control group clusters (p<0·0001), but this effect was not seen in mosquitoes captured 3 weeks after MDA. Overall entomological inoculation rates (EIRs; infectious bites per person per night) did not differ between groups (intervention EIR 0·010; control EIR 0·011; between-group ratio 0·91, 95% CI 0·56-1·30; p=0·45). In 2020, children aged 10 years and younger in the intervention group had a significantly higher increase in haemoglobin pre-intervention versus post-intervention than children in the control group (p=0·007).

INTERPRETATION

Repeated high-dose ivermectin MDA integrated with SMC distributions at the study site did not reduce malaria incidence among children relative to placebo MDA, despite evidence that, compared with the control group, mosquito survivorship in the first year was reduced in the intervention group the week following MDA and overall improvements in haemoglobin were greater in children in the intervention group. Confounding factors, including unexpectedly low malaria incidence over the trial period, possibly due to government distribution of dual-chemistry ITNs to all trial clusters in the middle of the intervention period, overdispersion of the primary incidence outcome between clusters, and high parasite and mosquito species diversity, might have influenced the primary outcome.

FUNDING

National Institute of Allergy and Infectious Diseases.