Efficacy of Wolbachia-mediated sterility for control of dengue: emulation of a cluster randomized target trial

Background Matings between male Aedes aegypti mosquitoes infected with wAlbB strain of Wolbachia and wildtype females yield non-viable eggs. We evaluated the efficacy of releasing wAlbB-infected Ae. aegypti male mosquitoes to suppress dengue. Methods We specified the protocol of a two-arm cluster-randomised test-negative controlled trial (cRCT) and emulated it using a nationally representative test-negative/positive database of individuals reporting for febrile illness to any public hospital, general practitioner or polyclinic. We built a cohort of individuals who reside in Wolbachia locations versus a comparator control group who do not reside in Wolbachia locations. We emulated a constrained randomisation protocol used in cRCTs to balance dengue risk between intervention and control arms in the pre-intervention period. We used the inverse-probability weighting approach to further balance the intervention and control groups using a battery of algorithmically selected sociodemographic, environmental and anthropogenic variables. Intention-to-treat analyses was conducted to estimate the risk reduction of dengue given Wolbachia exposure. Findings The final cohort consisted of 7,049 individuals residing in areas treated by Wolbachia interventions for at least 3 months and 69,216 individuals residing in non-treated areas in the same time period. Intention-to-treat analyses revealed that, compared with controls, Wolbachia releases for 3, 6, 12 or more months was associated to a 47% (Odds ratio (OR): 0.53 [0.45-0.62]), 47% (OR: 0.53 [0.50-0.65]) and 59% (OR: 0.41 [0.39-0.50]) protective efficacy against dengue respectively. When exposed to 12 or more months of Wolbachia releases, protective efficacy ranged from 36% (OR: 0.64 [0.58-0.96]) to 77% (OR: 0.23 [0.22-0.33]) dependent on township, and from 48% (OR: 0.52 [0.48-0.7]) to 78% (OR: 0.22 [0.09-0.32]) across years. The proportion of virologically confirmed dengue cases was lower overall in the intervention arm, and across each subgroup. Protective efficacies were found across all townships, years, age and sex subgroups, with higher durations of Wolbachia exposure similarly associated to greater risk reductions of dengue. Interpretation Our results demonstrated the potential of Wolbachia-mediated sterility for strengthening dengue control in tropical cities, where dengue burden is the greatest. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This study was supported by funding from Singapore's Ministry of Finance, Ministry of Sustainability and the Environment, National Environment Agency, and National Robotics Program. JTL is supported by the Ministry of Education (MOE), Singapore Start-up Grant. SB is supported by an MOE Tier 2 grant.   ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This project was exempted from formal bioethics review as it is not considered human biological research, as advised by the Ministry of Health, Singapore. All laboratory tests were performed for clinically directed reasons, and the data from these tests is routinely collected as part of routine dengue surveillance under the Infectious Disease Act, which exempts the need for informed consent. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors