SINGAPORE – Five young volunteers have been deliberately exposed to the Covid-19 virus in Singapore’s first human challenge study, opening doors for more such research to strengthen the country’s infectious disease response capabilities.
The study, known as Sing-CoV, is being conducted at the National Centre for Infectious Diseases (NCID).
Researchers aim to recruit a total of 20 healthy individuals aged 21 to 30 who have been vaccinated against Covid-19 by September or October, with follow-up appointments continuing for up to a year.
Historical Significance of Human Challenge Studies in Medical Research
Unlike traditional studies where subjects are infected naturally, human challenge studies intentionally expose volunteers to a virus in a controlled environment.
This approach allows researchers to gain more precise insights about infectious agents in less time, potentially accelerating the development of vaccines and therapeutics.
While challenge studies might sound new, they have been used since the dawn of modern medical science.
One of the earliest medical trials was British physician Edward Jenner’s challenge study of smallpox in the 1790s, which demonstrated the efficacy of the earliest smallpox vaccine that contributed to the eradication of smallpox in 1977.
Singapore’s Preparation for Future Pandemic Threats
“We need to continually strengthen Singapore’s preparedness and response to infectious diseases, including ‘Disease X’, a future disease that could result in a pandemic,” said Professor Vernon Lee, the incoming chief executive officer of the Communicable Diseases Agency (CDA).
CDA, a new public health agency focused on managing communicable diseases, will be formed on 1 April this year.
Future human challenge studies will be conducted by this agency.
Participant Compensation and Global Research Collaboration
The Sing-CoV study reimburses participants for their hospital stay during the viral challenge ($300 a day), as well as pre-screening, screening, and follow-up appointments.
This totals more than $6,000 per volunteer.
Associate Professor Barnaby Young, the principal investigator for Sing-CoV, explained that having this framework allows Singapore to next participate in a global Covid-19 challenge project.
This project seeks next-generation vaccines that can prevent severe disease and block transmission.
MUSICC Study: International Covid-19 Research Initiative
This global initiative, the Mucosal Immunity in Human Coronavirus Challenge (MUSICC) study, is led by Imperial College London.
Imperial College London conducted the world’s first Covid-19 human challenge study in 2021 with 36 participants.
NCID expects to begin recruitment for MUSICC in the second half of 2025.
The study will use the Omicron BA.5 strain rather than the Delta strain used in Sing-CoV.
Singapore’s foray into challenge studies could help promote research of other regionally endemic conditions like dengue in the future.
Scientific Advantages of Controlled Infection Studies
Human challenge studies provide unique advantages over traditional research methods.
Prof Young said: “When we are studying, for example, people with Covid-19… we don’t know how they were exposed, when they were exposed, exactly how much virus they were exposed to, and it’s very difficult to measure those time points afterwards.”
These studies are particularly useful for testing vaccine effectiveness as the infection is engineered, removing uncertainties about natural exposure.
They can be conducted quickly and cost-effectively with fewer participants.
Ethical Framework for Human Challenge Studies
The ethics of such studies was the topic of a recent workshop called “The Ethics of Human Challenge Studies”, which was jointly organised by the National University of Singapore’s Yong Loo Lin School of Medicine and NCID.
It brought together local and international experts to explore responsible conduct of challenge studies.
The same ethical requirements that govern all medical research apply to challenge studies, including obtaining informed consent, minimizing harms to participants, and ensuring scientific validity.
Safety Protocols and Participant Protection
In challenge studies, harm minimisation is especially important. This is achieved through careful selection of participants least likely to be badly harmed, close symptom monitoring, quick access to treatments, and keeping participants in a closed environment until they are no longer infectious.
Only competent adults who provide informed consent may be enrolled in challenge trials.
This allows participants to evaluate for themselves whether they feel comfortable with exposure to an infectious disease given the potential social benefits such studies might bring.
First-hand Experience: Singapore’s Pioneer Challenge Study Participant
Mr Goh Zhi Hao, 24, a mechanical engineering student at Nanyang Technological University, became the first participant in Sing-CoV. He joined after hearing about it through a connection at NCID.
He was quarantined for 14 days at NCID in September 2024. “The experience was better than I expected,” said Mr Goh, noting that his symptoms were mild and his accommodation was spacious and comfortable enough for studying.
He developed sore eyes and fatigue a day after receiving a small drop of purified Covid-19 virus in his nose, with symptoms lasting two to three days.
Safety Record of Human Challenge Studies
Of the five participants inoculated with SARS-CoV-2 so far, only Mr Goh and one other person became infected. Prof Young emphasized that the amount of virus administered is identical to that used in UK Covid-19 studies.
Participants are closely monitored by a dedicated healthcare team during their stay of up to 14 days.
A review of hundreds of challenge trials from 1980 to 2021, involving more than 15,000 participants, found no deaths. Only a fraction of a percent of participants experienced serious adverse events – a comparable or even more favorable risk level than many early phase clinical trials of novel therapeutics.
“Around 130 people have taken part in SARS-CoV-2 human challenge studies around the world now… and nobody’s had any severe adverse events, nobody has required antiviral medications or developed a severe infection,” Prof Young said.
Comprehensive Data Collection Methods
The research team collects comprehensive data from participants, including nose swabs, blood samples, stool samples, and even expired air.
Participants use a machine that they breathe into and sing to for air collection.
After the viral challenge, participants make five follow-up visits to NCID for check-ups.
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