SINGAPORE – To better understand how the human immune system responds to dengue, five volunteers were deliberately infected with the mosquito-borne virus in a new study by the National Centre for Infectious Diseases (NCID).
The study is part of a research programme that aims to accelerate the development of dengue treatments and vaccines.
It comes after another NCID study on Covid-19, in which five volunteers were deliberately exposed to the virus as part of efforts to strengthen Singapore’s disease preparedness and response.
Of the 85 people who volunteered for the new study, five participants – comprising four women and one man between the ages of 21 and 45 – were eventually selected.
The criteria include having no history of dengue infection and no vaccination against dengue or related diseases, such as yellow fever or Japanese encephalitis, said NCID clinical trial unit head Barnaby Young, who led the study.
Between March and May 2026, the participants received a weakened strain of the DENV-3 serotype of the dengue virus, developed by the National Institutes of Health in the United States.
They were quarantined at NCID for at least 10 days, during which they underwent various immunological, virological and safety assessments.
Researchers tracked the viral level in their bloodstream using polymerase chain reaction at multiple time points, allowing them to observe how the infection developed and resolved over the course of the illness. Regular blood tests and health assessments tracked the infection while ensuring participant safety at every stage.
As they were infected with a weakened virus, they developed mild symptoms such as rashes and headaches, but did not show more serious ones like fever or bleeding, said NCID senior staff nurse Koh Shi Yuen.
One participant, who wanted to be known only as Ong, said she did not experience any obvious symptoms and has since made a full recovery.
“I felt that participating was an opportunity to give back. Dengue affects so many people, and knowing that my involvement could help advance research and potentially improve outcomes for others made the experience deeply meaningful,” said the 31-year-old.
Over the next three years, NCID will conduct annual follow-up checks on the participants, who will also receive an optional dengue vaccine six months after infection during the study.
Controlled infections provide useful scientific data on the immune response and viral replication, Young noted.
“But the fundamental reason that these studies are done is to test vaccines and develop treatments, and bring them into clinical use faster than the traditional way in which these studies are done,” he said.
NCID hopes to work with pharmaceutical companies so that similar studies can be done to test the effectiveness of dengue vaccines and antivirals, he added.
Young noted that internationally, there are currently no clinically approved antiviral drugs for dengue.
Dengvaxia – the only dengue vaccine approved for use in Singapore – is being phased out after manufacturer Sanofi permanently discontinued it due to low global demand.
The study was funded by the Tripartite Programme in Infectious Diseases for New Discoveries and Treatment. That is an initiative by NHG Health, A*STAR and the Nanyang Technological University’s Lee Kong Chian School of Medicine to accelerate local research in infectious diseases.
In Singapore, dengue cases have seen a decline over the past year, with 819 cases here as of end-May 2026, according to National Environment Agency data. This is a 62 per cent drop from the 2,127 cases reported over the same period in 2025.
The decrease comes amid an expansion of Project Wolbachia , which aims to control the Aedes mosquito population here through the release of laboratory-grown male mosquitoes infected with Wolbachia bacteria.
Globally, there have been about 500,000 dengue cases as of end-March 2026, according to the European Centre for Disease Control and Prevention, down from 1.4 million over the same period in 2025.
Still, the risk of future outbreaks remains as more regions face dengue risks amid climate change and increasing urbanisation, said Young.
He added that future studies could potentially involve other dengue serotypes, or vaccinating participants before infecting them with dengue virus.
Zhaki Abdullah is a correspondent at The Straits Times. He is on the health beat, in addition to occasionally covering science, environmental, tech and Muslim affairs issues.
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