Dengue cases drop to 20-year low following large-scale releases of Wolbachia mosquitoes in the Aburrá Valley, Colombia

New research by the World Mosquito Program (WMP) and the University of Antioquia, published today in PLOS Neglected Tropical Diseases, shows dengue cases have dropped to the lowest level in 20 years across Colombia’s Aburrá Valley following large-scale releases of Wolbachia mosquitoes.

WMP’s city-wide deployments of Wolbachia mosquitoes between 2015 and 2022 in Bello, Medellín and Itagüi — protecting more than three million people — have seen dengue incidence rates drop by at least 95 per cent.

Dengue global surge

The findings arrive in a critical year which has seen the Americas already top 3.5 million cases of dengue — the second-highest annual incidence of the disease since 1980. Across the globe, there have been more than 4.5 million cases and over 4,000 dengue-related deaths reported from 80 countries/territories globally.

The largest contiguous implementation of Wolbachia mosquito releases to-date confirms WMP’s Wolbachia method is feasible and effective at a large scale.

“Dengue incidence has declined by 95-97% in the three cities since Wolbachia establishment, compared to the decade prior to Wolbachia releases, and dengue case numbers since 2020 have been at their lowest in twenty years,” says Professor Iván Darío Vélez, Director of PECET, University of Antioquia.
“It is notable that dengue incidence this year has exceeded epidemic alert levels in Colombia at a national level and in the majority of dengue-prone cities, but remains at historic low levels throughout the Wolbachia-treated cities of the Aburra Valley that are home to more than three million people.”

A sustainable solution

WMP’s groundbreaking Wolbachia solution for protecting communities from mosquito-borne diseases, is a one-time, safe and cost-effective method, which has been deployed in 14 countries over the past decade. A natural bacteria found in half of all insect species, Wolbachia blocks the transmission of viruses when introduced into Aedes aegypti mosquitoes.

The effectiveness of Wolbachia for controlling dengue has been demonstrated in multiple field trials. More than 11 million people in Asia-Pacific and Latin America are already benefiting from this protection in communities where Wolbachia has been released.

Short-term releases of Wolbachia mosquitoes in dengue-affected communities allow Wolbachia to spread into the local mosquito population, effectively shielding it against dengue and other viruses. Once established, Wolbachia remains in the local mosquitoes for years without additional releases.

Effective at scale

Over the seven years of releases in the Aburrá Valley, a total of just over 88 million Wolbachia mosquitoes were released, with Wolbachia established throughout the target mosquito populations.

Alongside monitoring of dengue cases reported to public health authorities, WMP conducted a case-control study in primary care clinics in northeast Medellín between 2019 and 2021. This found that dengue incidence was reduced by half among participants resident in Wolbachia-treated neighbourhoods compared to neighbourhoods where Wolbachia had not yet been released.

These results support WMP’s previous findings, most notably in Yogyakarta, Indonesia. WMP’s gold-standard randomised trial in the Indonesian city showed a 77% reduction in dengue incidence and an 86% reduction in dengue hospitalisations in Wolbachia treated areas compared with untreated areas. Efficacy was equivalent for all four dengue virus serotypes.

“These results demonstrate that city-wide deployment of Wolbachia to protect large urban populations is feasible and effective. The substantial public health impact observed in Medellín, Bello and Itagüí is consistent with that reported previously from deployments in Brazil, Indonesia and Australia,” says Dr Katie Anders, Director of Impact Assessment.

“The case control study results support the conclusion that the majority of the recent decline in dengue in the three cities is directly attributable to Wolbachia.”

Cost effectiveness

A recent economic evaluation of Wolbachia deployment in 11 cities in Colombia, found that in nine of these cities the healthcare costs saved through fewer dengue cases would be sufficient to offset the costs of Wolbachia deployment within 10 years. Counting the economic benefits from both averted medical costs and human capital gains, Wolbachia was predicted to return USD 5.61 for every dollar invested, equating to a break-even time of only 1.43 years (17 months) in Cali and 1.69 years (20 months) nationally.

“Large dengue outbreaks occur every two to five years in Colombia, and communities and governments currently have limited tools and resources to prevent or respond effectively to these surges in cases,” says Dr Anders.

“What makes Wolbachia different from — and more cost-effective than — conventional vector control is that after an initial investment to implement, there is sustained community-wide protection against mosquito-borne diseases without any ongoing investment of resources or behaviour change required. Because the health and economic benefits accumulate over time, Wolbachia is a long-term solution that can pay for itself.”

The papers can be found at the links below.