Reasons for Sharp Decline in Dengue Cases Reported in 2025

12 Mr Ang Wei Neng asked the Minister for Sustainability and the Environment (a) what are the major reasons for the sharp decline in the number of dengue cases reported in 2025; and (b) when will the Project Wolbachia trial be extended to all the towns in Singapore.

The Senior Parliamentary Secretary to the Minister for Sustainability and the Environment (Ms Goh Hanyan) (for the Minister for Sustainability and the Environment): Sir, 4,036 dengue cases were reported in 2025, which was the lowest number since 2018. An absence of major local outbreaks locally, the global decline in dengue cases in 2025 and concerted efforts by all stakeholders and residents in Singapore to control the mosquito population, collectively contributed to the decrease. The National Environment Agency's (NEA's) holistic dengue control strategy, which combines Project Wolbachia, vector control operations and actions by all to keep premises free of mosquito breeding, continue to help keep dengue incidence low.

By March 2026, Project Wolbachia will be expanded to cover 740,000 households, up from 580,000 households in April 2025. By end-2026, Project Wolbachia will be released to cover 800,000 households or 50% of all households in Singapore, covering the majority of areas at risk of large dengue outbreaks. NEA will continue to monitor the progress of Project Wolbachia and adjust its deployment strategy.

Reducing dengue risks in our community requires the cooperation and support of residents. We seek residents' understanding that more mosquitoes may be seen during the release periods of male Wolbachia-carrying mosquitoes, but these mosquitoes are necessary to help suppress the Aedes Aegypti population and do not bite or transmit disease.

Mr Speaker: Mr Ang.

Mr Ang Wei Neng (West Coast-Jurong West): Thank you, Speaker. Can I ask a supplementary question? How effective is this Wolbachia trial? Is it the main reason for the significant drop in dengue cases last year?

If so, I would ask another supplementary question. Because at one point, Nanyang was considered a dengue red zone and quite a number of residents shared with me the agony of getting dengue fever. I have appealed to NEA to extend the Wolbachia trial to Nanyang, which is in Jurong West. And indeed, NEA has extended the trial to Jurong West, but stopped short of reaching Nanyang. So, I have also checked the NEA website just a while ago to confirm this, the extension of the trial.

Since NEA has considered the Wolbachia trial to be effective, what is the bottleneck that is preventing NEA from expanding the Wolbachia trial faster to Nanyang and the rest of Singapore? And even by the end of this year, NEA is only covering 50% of households. So, how could NEA add more resources to expand the trial of Wolbachia faster and better?

Ms Goh Hanyan: I thank the Member for his supplementary questions. He had a couple, so I will answer the first one on whether Project Wolbachia was the main reason for the decline in dengue cases in 2025. As I shared, Project Wolbachia is part of NEA's comprehensive strategy to suppress mosquito population and manage dengue risk. It has demonstrated good performance, as the Member has highlighted, reducing the risks of dengue transmission by more than 70% in release areas. So, that is a pretty good result.

However, I would also like to say that it is not a silver bullet for suppressing the mosquito population and managing dengue risk. Sustained vigilance and collective responsibility by the community is important to prevent mosquito breeding and remains critical to reduce the risk of dengue transmission. Globally, in 2025, we also saw a decrease in dengue cases from 14.4 million for the year before, to five million; and locally, as I said just now, there is absence of local clusters as well.

All of this, collectively, including the combined impact of NEA's comprehensive strategy, rather than that as a single intervention, has helped to lower the number of dengue cases. In short, it is one of the reasons, but it is not the only reason why we are seeing a decline last year.

On the other question, I thank the Member for raising the request on behalf of his residents. In terms of site selection, site selection on areas to receive the Wolbachia Aedes mosquito release is based on multiple considerations, including historical dengue situations and the current Aedes Aegypti mosquito population. So, there are many factors in play and it is on a relative basis across different locations in Singapore. NEA will announce the new sites in due course, so we take note of the Member's request.

The other question was around what are the constraints? Resources are finite and so the pace of expansion is also influenced by how quickly mosquito populations can be suppressed, which depends on the local mosquito situation and prevalence of mosquito breeding habitats.

So, it is a matter of figuring out how effective our current site releases have been. This is a dynamic situation. And then, on a forward-looking basis, figuring out which sites, then, have a higher incidence and also, the local population of these mosquitoes, for us to decide when the sites will be expanded into.

So, in due course, we will be announcing where the new sites will be as we lead up to further expansions towards the end of the year.