Background: Aedes aegypti mosquitoes infected with Wolbachia pipientis ( w Mel strain) have reduced potential to transmit dengue viruses. Methods: We conducted a cluster randomised trial of deployments of w Mel-infected Ae. aegypti for control of dengue in Yogyakarta City, Indonesia. Twenty-four geographic clusters were randomly allocated to receive w Mel deployments as an adjunct to local mosquito control measures; or to continue with local mosquito control measures only. A test-negative design was used to measure efficacy. Study participants were persons 3–45 years old attending primary care clinics with acute undifferentiated fever. Laboratory testing identified virologically-confirmed dengue cases and test-negative controls. The primary endpoint was efficacy of w Mel in reducing the incidence of symptomatic, virologically-confirmed dengue, caused by any dengue virus serotype. Results: Following successful introgression of w Mel in intervention clusters, 8144 participants were enrolled; 3721 from w Mel-treated clusters and 4423 from untreated clusters. In the ITT analysis virologically-confirmed dengue occurred in 67 of 2905 (2.3%) participants in the w Mel-treated and 318 of 3401 (9.4%) in the untreated arm (OR 0.23, 95% CI, 0.15 to 0.35; P=0.004): protective efficacy of 77.1% (95% CI, 65.3 to 84.9). Protective efficacy was similar for the four serotypes. Hospitalisation for virologically-confirmed dengue was less frequent for participants resident in the w Mel-treated (13/2905, 2.8%) compared to the untreated arm (102/3401, 6.3%): protective efficacy 86.2% (95% CI, 66.2 to 94.3) Conclusions: w Mel introgression into Ae. aegypti populations was efficacious in reducing the incidence of symptomatic dengue, and also led to fewer dengue hospitalisations. Trial registration number: ClinicalTrials.gov Identifier: NCT03055585 and INA-A7OB6TW

Background: Ae. aegypti mosquitoes stably transfected with the intracellular bacterium Wolbachia pipientis (wMel strain) have been deployed for biocontrol of dengue and related arboviral diseases in multiple countries. Field releases in northern Australia have previously demonstrated near elimination of local dengue transmission from Wolbachia-treated communities, and pilot studies in Indonesia have demonstrated the feasibility and acceptability of the method. We conducted a quasi-experimental trial to evaluate the impact of scaled Wolbachia releases on dengue incidence in an endemic setting in Indonesia. Methods: In Yogyakarta City, Indonesia, following extensive community engagement, wMel Wolbachia-carrying mosquitoes were released every two weeks for 13–15 rounds over seven months in 2016–17, in a contiguous 5 km2 area (population 65,000). A 3 km2 area (population 34,000) on the opposite side of the city was selected a priori as an untreated control area. Passive surveillance data on notified hospitalised dengue patients was used to evaluate the epidemiological impact of Wolbachia deployments, using controlled interrupted time-series analysis. Results: Rapid and sustained introgression of wMel Wolbachia into local Ae. aegypti populations was achieved. Thirty-four dengue cases were notified from the intervention area and 53 from the control area (incidence 26 vs 79 per 100,000 person-years) during 24 months following Wolbachia deployment. This corresponded in the regression model to a 73% reduction in dengue incidence (95% confidence interval 49%,86%) associated with the Wolbachia intervention. Exploratory analysis including 6 months additional post-intervention observations showed a small strengthening of this effect (30 vs 115 per 100,000 person-years; 76% reduction in incidence, 95%CI 60%,86%). Conclusions: We demonstrate a significant reduction in dengue incidence following successful introgression of Wolbachia into local Ae. aegypti populations in an endemic setting in Indonesia. These findings are consistent with previous field trials in northern Australia, and support the effectiveness of this novel approach for dengue control.

Background The introduction of the bacterium Wolbachia (wMel strain) into Aedes aegypti mosquitoes reduces their capacity to transmit dengue and other arboviruses. Evidence of a reduction in dengue case incidence following field releases of wMel-infected Ae. aegypti has been reported previously from a cluster randomised controlled trial in Indonesia, and quasi-experimental studies in Indonesia and northern Australia. Methodology/Principal findings Following pilot releases in 2015–2016 and a period of intensive community engagement, deployments of adult wMel-infected Ae. aegypti mosquitoes were conducted in Niterói, Brazil during 2017–2019. Deployments were phased across four release zones, with a total area of 83 km2 and a residential population of approximately 373,000. A quasi-experimental design was used to evaluate the effectiveness of wMel deployments in reducing dengue, chikungunya and Zika incidence. An untreated control zone was pre-defined, which was comparable to the intervention area in historical dengue trends. The wMel intervention effect was estimated by controlled interrupted time series analysis of monthly dengue, chikungunya and Zika case notifications to the public health surveillance system before, during and after releases, from release zones and the control zone. Three years after commencement of releases, wMel introgression into local Ae. aegypti populations was heterogeneous throughout Niterói, reaching a high prevalence (>80%) in the earliest release zone, and more moderate levels (prevalence 40–70%) elsewhere. Despite this spatial heterogeneity in entomological outcomes, the wMel intervention was associated with a 69% reduction in dengue incidence (95% confidence interval 54%, 79%), a 56% reduction in chikungunya incidence (95%CI 16%, 77%) and a 37% reduction in Zika incidence (95%CI 1%, 60%), in the aggregate release area compared with the pre-defined control area. This significant intervention effect on dengue was replicated across all four release zones, and in three of four zones for chikungunya, though not in individual release zones for Zika. Conclusions/Significance We demonstrate that wMel Wolbachia can be successfully introgressed into Ae. aegypti populations in a large and complex urban setting, and that a significant public health benefit from reduced incidence of Aedes-borne disease accrues even where the prevalence of wMel in local mosquito populations is moderate and spatially heterogeneous. These findings are consistent with the results of randomised and non-randomised field trials in Indonesia and northern Australia, and are supportive of the Wolbachia biocontrol method as a multivalent intervention against dengue, chikungunya and Zika.

Intervention trials of vector control methods often require community level randomization with appropriate inferential methods. For many interventions, the possibility of confounding due to the effects of health-care seeking behavior on disease ascertainment remains a concern. The test-negative design, a variant of the case-control method, was introduced to mitigate this issue in the assessment of the efficacy of influenza vaccination (measured at an individual level) on influenza infection. Here, we introduce a cluster-randomized test-negative design that includes randomization of the intervention at a group level. We propose several methods for estimation and inference regarding the relative risk (RR). The inferential methods considered are based on the randomization distribution induced by permuting intervention assignment across two sets of randomly selected clusters. The motivating example is a current study of the efficacy of randomized releases of Wolbachia-infected Aedes aegypti mosquitoes to reduce the incidence of dengue in Yogyakarta City, Indonesia. Estimation and inference techniques are assessed through a simulation study.