Immune System Responses and Trained Immunity After AS01 AdministrationPhase 2NCT07527247
Improving Vaccine Protection for Adults
A Phase 2 study testing AS01 adjuvant (0.5 mL intramuscular) and YF17D (Stamaril, Sanofi-Pasteur) in people with Immune System Responses and Trained Immunity After AS01 Administration and Healthy Adult, run by Singapore General Hospital at 1 site in Singapore.
Trial summary
As people grow older, their immune system - the body's natural defence against diseases - becomes weaker, making them more vulnerable to infections and less responsive to vaccines. This was clearly seen during the COVID-19 pandemic, where older adults were more likely to develop severe illness. Read more about this study
- Who is it for?
- Ages 21 to 59 yearsHealthy volunteers can take part
- Conditions the study is for
- Immune System Responses and Trained Immunity After AS01 Administration, Healthy Adult
- What is being tested?
- AS01 adjuvant (0.5 mL intramuscular) and YF17D (Stamaril, Sanofi-Pasteur)
- Type of treatment
- Vaccines, Injection or infusion
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 40 participants
- Where
- 1 siteSingapore
- Study dates
- 6 Nov 2025to 28 Feb 2029
- Phase
- Phase 2
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 21 to 59 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- Adults aged 21 to 59 years of age at time of screening.
- BMI 18.5 - 27.5 kg / m2 (BMI values for Asian population according to MOH guideline NIH Consensus Conference).
- Satisfactory baseline medical assessment as assessed by physical examination and a stable health status. For subjects with underlying comorbidities, the conditions must be deemed stable by the investigators, and they must not have any hospitalisation relating to these conditions in the last 6 months.
- Voluntarily participate, understand and sign an informed consent form approved by the Ethical Review Board.
- Subjects who are willing to comply with the requirements of the study protocol and scheduled visits. These requirements include completion of the subject diary, return for follow-up visits. Subjects should also be willing to make themselves available for the duration of the study, with access to a consistent means of contact.
- Accessible vein at the forearm for blood taking.
- Female subjects of non-childbearing potential due to surgical sterilisation (hysterectomy or bilateral oophorectomy or tubal ligation) or menopause. Post-menopausal subjects must have had at least 12 months of natural (spontaneous) amenorrhoea.
Who cannot join
- Previous vaccination against yellow fever, dengue either with a registered product or from participation in a previous vaccine study.
- Previously received AS01-adjuvanted vaccines (e.g. Recombinant zoster vaccine, RTS,S/AS01, RSVPre-F3-AS01), either with a registered product or from participation in a previous vaccine study.
- Planned administration of a AS01-adjuvanted vaccine or yellow fever vaccine other than the study vaccine during the study.
- Subjects who have been unwell in the last 7 days prior to screening.
- History of documented yellow fever and / or dengue infection.
- Dengue seropositivity upon screening.
Show all 29Show fewer
- History of smoking within the last 1 year.
- Planned travel to yellow fever endemic countries during the study.
- Known allergy to AS01 and YF17D vaccine or their components (e.g. egg products).
- Diagnosis of diabetes HBA1c > 6.5 according to American Diabetes Association criteria62.
- Any medical condition that in the judgment of the investigator will make intramuscular injection unsafe (e.g. thrombocytopenia with platelet count < 50x10^9/L, coagulopathy, anti-coagulant therapy).
- Risk factor for live-attenuated vaccines, including any confirmed or suspected primary or acquired immunodeficiency based on history and physical examination:
- History of thymus gland disease
- Haematologic neoplasms including leukaemia, lymphoma, myelodysplastic syndromes
- Diagnosed with cancer or treatment for cancer (except for localised basal cell carcinoma) within 3 years prior to screening
- Post-transplant: solid organ and haematopoietic stem cell transplant
- Immunocompromised due to primary or acquired (including HIV/AIDS) immunodeficiency
- Other significantly immunocompromising conditions
- Administration of anti-inflammatory drugs for the past 7 days (e.g. NSAIDs, Paracetamol, aspirin).
- Use of metformin for the last 1 month.
- Use of corticosteroids within the last 6 months prior to the first vaccine dose (defined as prednisolone > 10 mg / day or equivalent for > 2 weeks, or prednisolone > 40mg / day or > 1 week). Inhaled and topical steroids are allowed.
- Received biologics (such as anti-TNF inhibitors, IL-1 inhibitors, co-stimulation blockers, B-cell depleting therapy) for the last 12 months.
- Any condition (e.g. extensive psoriasis, chronic pain syndrome, severe hearing loss, cognitive impairment, dialysis, autoimmune disorders) that in the opinion of the investigator, would complicate or compromise the study or wellbeing of the subject, or prevent completion of the study.
- Evidence of substance abuse, or previous substance abuse.
- Clinically significant anaemia (Hb < 10 g/dL).
- Blood donation exceeding > 450 ml in the past 3 months.
- Participation in a study involving administration of an investigational or non-investigational compound within the past four months or planned participation during the duration of this study.
- Administration of any licensed vaccine within 30 days before the first study vaccine dose or planned to receive such products within 30 days after the study vaccination.
- Received immunoglobulin or any blood products within the 90 days preceding the first dose of study vaccine or planned to receive such products during the study period.
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
Singapore1 site, 1 recruiting
- Recruiting
Singapore General Hospital
Singapore, 169608
Candice Y.Y. Chan, MBChB, MRCP, +6563213479, candice.chan.y.y@singhealth.com.sg
Christina Titin, +6565762802, christina.titin@singhealth.com.sg
About this study
Official title: Using AS01 Adjuvant to Improve Immune Response in Older Adults Through Trained Immunity
As people grow older, their immune system - the body's natural defence against diseases - becomes weaker, making them more vulnerable to infections and less responsive to vaccines. This was clearly seen during the COVID-19 pandemic, where older adults were more likely to develop severe illness. Researchers have made an interesting discovery about AS01, an ingredient already used in successful vaccines like the shingles vaccine. They found clues that AS01 might work like a general fitness trainer for the immune system, potentially making it stronger and better at fighting off various types of infections, not just specific ones. To confirm this possibility, we are conducting this research study with adults aged 21-59 to test whether AS01 by itself can boost and train the immune system, how long this boost lasts, and if it actually helps you fight off other infections more effectively.
Read the detailed description
As people age, the immune system becomes less responsive, increasing susceptibility to infections and reducing vaccine responsiveness. AS01 is a liposome-based adjuvant used in licensed vaccines (e.g., shingles vaccine) that activates innate and adaptive immunity. Emerging evidence suggests AS01 may also induce trained immunity, a form of innate immune reprogramming that could enhance protection against unrelated infections. This study tests whether AS01 given alone can boost and train the immune system in healthy adults, how long these effects last, and whether this translates into better control of a heterologous viral challenge.
This will be a single-center, randomised, single-blind, placebo-controlled experimental medicine study at Singapore General Hospital (N=40; ages 21-59). Participants receive a single intramuscular dose of AS01 (0.5 mL) or saline placebo on Day 0. To model a controlled viral exposure, all participants then receive the licensed live-attenuated yellow fever vaccine (YF17D, Stamaril) either at 1 month (Day 30) or 3 months (Day 90) after AS01/placebo, per randomization. Serial blood sampling measures immune reprogramming, durability, and response to the viral challenge over ~2 or 4 months depending on assignment
Findings may clarify whether AS01 can be used as a standalone immune booster to rapidly enhance broad protection. Information that could be useful for outbreak preparedness, especially before pathogen-specific vaccines are available.
Therefore, (1) Early and durable innate immune changes after AS01 (e.g., gene expression and epigenetic markers in myeloid/innate cells); (2) YF17D viremia (RNAemia) after vaccination as an indicator of heterologous viral control; and (3) T-cell and B-cell responses to YF17D and how they relate to viremia, will be measured and analysed.
AS01 and YF17D are licensed components when used with their indicated vaccines. Common reactions include local injection-site symptoms and short-lived systemic symptoms; rare serious adverse events have been reported with YF17D. Participants are monitored and provided safety guidance and contact pathways throughout the study.
- Being tested
- AS01 adjuvant (0.5 mL intramuscular), YF17D (Stamaril, Sanofi-Pasteur), Placebo (NaCl 09%, 0.5mL)
- Keywords
- AS01, AS01 adjuvant, Immune durability, Immune system, Immune response modulation, Recombinant zoster vaccine adjuvant, Vaccine, Randomized, Placebo-controlled, Blinded, Healthy volunteers, Protective effects, Yellow Fever Vaccine
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
AS01 adjuvant (0.5 mL intramuscular)Biological
The AS01 suspension contains 50 mcg/micrograms of 3-O-desacyl-4'monophosphoryl lipid A (MPL) and 50 mcg/micrograms of Quillaja Saponaria Molina, fraction 21 (QS21), licensed by GSK, available as a separate vial from the licensed Shingrix vaccine.
YF17D (Stamaril, Sanofi-Pasteur)Biological
Also called YF17D, yellow fever vaccine
Stamaril, the live-attenuated yellow fever vaccine, utilises the YF17D strain. Stamaril is supplied in the form of powder and solvent for suspension for injection in pre-filled syringe, Yellow fever vaccine (live).
Placebo (NaCl 09%, 0.5mL)Other
Also called Placebo, Saline placebo, Saline injection
The placebo will consist of 0.9% saline solution in equivalent volume.
| Study group | Role | What they receive |
|---|---|---|
| AS01 + YF17D at 1 Month | Experimental | Participants receive AS01 (0.5 mL IM on Day 0) and yellow fever vaccine YF17D on Day 30. Receives: Biological: AS01 adjuvant (0.5 mL intramuscular); Biological: YF17D (Stamaril, Sanofi-Pasteur) |
| AS01 + YF17D at 3 Months | Experimental | Participants receive AS01 (0.5 mL IM on Day 0) and yellow fever vaccine YF17D on Day 90. Receives: Biological: AS01 adjuvant (0.5 mL intramuscular); Biological: YF17D (Stamaril, Sanofi-Pasteur) |
| Placebo + YF17D at 1 Month | Placebo comparator | Participants receive placebo (0.9% saline, 0.5 mL IM on Day 0) and yellow fever vaccine YF17D on Day 30. Receives: Biological: YF17D (Stamaril, Sanofi-Pasteur); Other: Placebo (NaCl 09%, 0.5mL) |
| Placebo + YF17D at 3 Months | Placebo comparator | Participants receive placebo (0.9% saline, 0.5 mL IM on Day 0) and yellow fever vaccine YF17D on Day 90. Receives: Biological: YF17D (Stamaril, Sanofi-Pasteur); Other: Placebo (NaCl 09%, 0.5mL) |
What is being measured
The primary outcome is the main question the study is designed to answer.
Host Immune Response
Explorative evaluation of host immune response profile (cytokines, immune cell populations, gene expression, epigenetic modifications) induced by AS01 versus placebo, using panel of validated multi-omics assay tests, over a 3-month period.
Measured: Days 0, 7, 14, 28, 56, 84 (3 months)
Secondary outcomes (3)
Viraemia Levels
Measure Yellow Fever viraemia levels via quantitative RT-PCR and calculate area under the curve (AUC) up to 7 days following yellow fever vaccine administration in AS01 versus placebo recipients.
Measured: 7 days following yellow fever vaccine administration
B Cell Response
Assess B cell responses to yellow fever by measurement of neutralising antibodies titres using plaque reduction neutralization test (PRNT) with sera at day 30 compared with pre-vaccination day 0, following yellow fever vaccine administration in AS01 versus placebo recipients.
Measured: 30 days
T Cell Response
Assess T cell responses to yellow fever vaccine using virus-specific IFNγ ELISPOT assay, with results expressed as spot-forming units (SFU) per 10^6 PBMCs at day 14 and day 30 versus pre-vaccination at day 9 in AS01 versus placebo recipients.
Measured: 30 days
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted14 Apr 2026
- Study start6 Nov 2025
- Primary completion28 Feb 2029 (estimated)
- Study completion28 Feb 2029 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (74)Papers the sponsor has linked to this study.
- Other trials for Immune System Responses and Trained Immunity After AS01 AdministrationStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 2
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- Participants are randomized in a 1:1:1:1 parallel assignment to one of four groups defined by (1) AS01 vs placebo at Day 0 and (2) timing of yellow fever vaccine administration at Day 30 or Day 90.
- Masking
- Single blind
- Who is masked
- Participant
- Enrolment
- 40 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Singapore General Hospital
- Sponsor type
- University, hospital or other
- Collaborators
- A*STAR Infectious Diseases Labs
- Responsible party
- Sponsor
- Investigators
- Candice Y.Y. Chan, MBChB, MRCP, Principal investigator, Singapore General HospitalAmit Singhal, B.Sc., M.Sc., Ph.D., Principal investigator, A*Star
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07527247
- Sponsor's protocol ID
- AS01-YF-01
- Other IDs
- CIRG25jan-0068
- Status last verified
- Jun 2026
- First submitted
- 4 Mar 2026
- Last updated
- 15 Jun 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Undecided
Publications
Mok DZL, Chan KR. The Effects of Pre-Existing Antibodies on Live-Attenuated Viral Vaccines. Viruses. 2020 May 8;12(5):520. doi: 10.3390/v12050520.
PubMed 32397218Yau C, Gan ES, Kwek SS, Tan HC, Ong EZ, Hamis NZ, Rivino L, Chan KR, Watanabe S, Vasudevan SG, Ooi EE. Live vaccine infection burden elicits adaptive humoral and cellular immunity required to prevent Zika virus infection. EBioMedicine. 2020 Nov;61:103028. doi: 10.1016/j.ebiom.2020.103028. Epub 2020 Oct 9.
PubMed 33045466Tan AT, Linster M, Tan CW, Le Bert N, Chia WN, Kunasegaran K, Zhuang Y, Tham CYL, Chia A, Smith GJD, Young B, Kalimuddin S, Low JGH, Lye D, Wang LF, Bertoletti A. Early induction of functional SARS-CoV-2-specific T cells associates with rapid viral clearance and mild disease in COVID-19 patients. Cell Rep. 2021 Feb 9;34(6):108728. doi: 10.1016/j.celrep.2021.108728. Epub 2021 Jan 21.
PubMed 33516277Kalimuddin S, Tham CYL, Qui M, de Alwis R, Sim JXY, Lim JME, Tan HC, Syenina A, Zhang SL, Le Bert N, Tan AT, Leong YS, Yee JX, Ong EZ, Ooi EE, Bertoletti A, Low JG. Early T cell and binding antibody responses are associated with COVID-19 RNA vaccine efficacy onset. Med. 2021 Jun 11;2(6):682-688.e4. doi: 10.1016/j.medj.2021.04.003. Epub 2021 Apr 8.
PubMed 33851143Bollampalli VP, Harumi Yamashiro L, Feng X, Bierschenk D, Gao Y, Blom H, Henriques-Normark B, Nylen S, Rothfuchs AG. BCG Skin Infection Triggers IL-1R-MyD88-Dependent Migration of EpCAMlow CD11bhigh Skin Dendritic cells to Draining Lymph Node During CD4+ T-Cell Priming. PLoS Pathog. 2015 Oct 6;11(10):e1005206. doi: 10.1371/journal.ppat.1005206. eCollection 2015 Oct.
PubMed 26440518Love MI, Huber W, Anders S. Moderated estimation of fold change and dispersion for RNA-seq data with DESeq2. Genome Biol. 2014;15(12):550. doi: 10.1186/s13059-014-0550-8.
PubMed 25516281Chan KR, Gan ES, Chan CYY, Liang C, Low JZH, Zhang SL, Ong EZ, Bhatta A, Wijaya L, Lee YH, Low JG, Ooi EE. Metabolic perturbations and cellular stress underpin susceptibility to symptomatic live-attenuated yellow fever infection. Nat Med. 2019 Aug;25(8):1218-1224. doi: 10.1038/s41591-019-0510-7. Epub 2019 Jul 15.
PubMed 31308506Mok DZ, Tng DJ, Yee JX, Chew VS, Tham CY, Ooi JS, Tan HC, Zhang SL, Lin LZ, Ng WC, Jeeva LL, Murugayee R, Goh KK, Lim TP, Cui L, Cheung YB, Ong EZ, Chan KR, Ooi EE, Low JG. Electron transport chain capacity expands yellow fever vaccine immunogenicity. EMBO Mol Med. 2024 Jun;16(6):1310-1323. doi: 10.1038/s44321-024-00065-7. Epub 2024 May 14.
PubMed 38745062Chan CY, Chan KR, Chua CJ, Nur Hazirah S, Ghosh S, Ooi EE, Low JG. Early molecular correlates of adverse events following yellow fever vaccination. JCI Insight. 2017 Oct 5;2(19):e96031. doi: 10.1172/jci.insight.96031.
PubMed 28978802Schep AN, Wu B, Buenrostro JD, Greenleaf WJ. chromVAR: inferring transcription-factor-associated accessibility from single-cell epigenomic data. Nat Methods. 2017 Oct;14(10):975-978. doi: 10.1038/nmeth.4401. Epub 2017 Aug 21.
PubMed 28825706Shaw AC, Goldstein DR, Montgomery RR. Age-dependent dysregulation of innate immunity. Nat Rev Immunol. 2013 Dec;13(12):875-87. doi: 10.1038/nri3547. Epub 2013 Oct 25.
PubMed 24157572Iwasaki A, Medzhitov R. Control of adaptive immunity by the innate immune system. Nat Immunol. 2015 Apr;16(4):343-53. doi: 10.1038/ni.3123.
PubMed 25789684Jo N, Hidaka Y, Kikuchi O, Fukahori M, Sawada T, Aoki M, Yamamoto M, Nagao M, Morita S, Nakajima TE, Muto M, Hamazaki Y. Impaired CD4+ T cell response in older adults is associated with reduced immunogenicity and reactogenicity of mRNA COVID-19 vaccination. Nat Aging. 2023 Jan;3(1):82-92. doi: 10.1038/s43587-022-00343-4. Epub 2023 Jan 12.
PubMed 37118516Hou Y, Chen M, Bian Y, Hu Y, Chuan J, Zhong L, Zhu Y, Tong R. Insights into vaccines for elderly individuals: from the impacts of immunosenescence to delivery strategies. NPJ Vaccines. 2024 Apr 10;9(1):77. doi: 10.1038/s41541-024-00874-4.
PubMed 38600250Esmaeili ED, Azizi H, Sarbazi E, Khodamoradi F. The global case fatality rate due to COVID-19 in hospitalized elderly patients by sex, year, gross domestic product, and continent: A systematic review, meta-analysis, and meta-regression. New Microbes New Infect. 2023 Jan;51:101079. doi: 10.1016/j.nmni.2022.101079. Epub 2023 Jan 4.
PubMed 36618974
Study at a glance
From the registry record, last updated by the sponsor on 15 Jun 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Using AS01 Adjuvant to Improve Immune Response in Older Adults Through Trained Immunity
- ClinicalTrials.gov ID
- NCT07527247
- Acronym / sponsor ID
- AS01-YF-01
- Keywords
- AS01, AS01 adjuvant, Immune durability, Immune system, Immune response modulation, Recombinant zoster vaccine adjuvant, Vaccine, Randomized
- Phase
- Phase 2
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 40 participants (estimated)
- Lead sponsor
- Singapore General HospitalUniversity, hospital or other
- Collaborators
- A*STAR Infectious Diseases Labs
- Study start
- 6 Nov 2025 (actual)
- Primary completion
- 28 Feb 2029 (estimated)
- Study completion
- 28 Feb 2029 (estimated)
- First posted
- 14 Apr 2026 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
As people grow older, their immune system - the body's natural defence against diseases - becomes weaker, making them more vulnerable to infections and less responsive to vaccines. This was clearly seen during the COVID-19 pandemic, where older adults were more likely to develop severe illness. Researchers have made an interesting discovery about AS01, an ingredient already used in successful vaccines like the shingles vaccine. They found clues that AS01 might work like a general fitness trainer for the immune system, potentially making it stronger and better at fighting off various types of infections, not just specific ones. To confirm this possibility, we are conducting this research study with adults aged 21-59 to test whether AS01 by itself can boost and train the immune system, how long this boost lasts, and if it actually helps you fight off other infections more effectively.
Detailed description
As people age, the immune system becomes less responsive, increasing susceptibility to infections and reducing vaccine responsiveness. AS01 is a liposome-based adjuvant used in licensed vaccines (e.g., shingles vaccine) that activates innate and adaptive immunity. Emerging evidence suggests AS01 may also induce trained immunity, a form of innate immune reprogramming that could enhance protection against unrelated infections. This study tests whether AS01 given alone can boost and train the immune system in healthy adults, how long these effects last, and whether this translates into better control of a heterologous viral challenge.
This will be a single-center, randomised, single-blind, placebo-controlled experimental medicine study at Singapore General Hospital (N=40; ages 21-59). Participants receive a single intramuscular dose of AS01 (0.5 mL) or saline placebo on Day 0. To model a controlled viral exposure, all participants then receive the licensed live-attenuated yellow fever vaccine (YF17D, Stamaril) either at 1 month (Day 30) or 3 months (Day 90) after AS01/placebo, per randomization. Serial blood sampling measures immune reprogramming, durability, and response to the viral challenge over ~2 or 4 months depending on assignment
Findings may clarify whether AS01 can be used as a standalone immune booster to rapidly enhance broad protection. Information that could be useful for outbreak preparedness, especially before pathogen-specific vaccines are available.
Therefore, (1) Early and durable innate immune changes after AS01 (e.g., gene expression and epigenetic markers in myeloid/innate cells); (2) YF17D viremia (RNAemia) after vaccination as an indicator of heterologous viral control; and (3) T-cell and B-cell responses to YF17D and how they relate to viremia, will be measured and analysed.
AS01 and YF17D are licensed components when used with their indicated vaccines. Common reactions include local injection-site symptoms and short-lived systemic symptoms; rare serious adverse events have been reported with YF17D. Participants are monitored and provided safety guidance and contact pathways throughout the study.
Study design
- Primary purpose
- Prevention
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Single blind (participant)
- Number of arms
- 4
- Model description
- Participants are randomized in a 1:1:1:1 parallel assignment to one of four groups defined by (1) AS01 vs placebo at Day 0 and (2) timing of yellow fever vaccine administration at Day 30 or Day 90.
| Arm | Type | Receives |
|---|---|---|
| AS01 + YF17D at 1 Month | Experimental | Biological: AS01 adjuvant (0.5 mL intramuscular), Biological: YF17D (Stamaril, Sanofi-Pasteur)Participants receive AS01 (0.5 mL IM on Day 0) and yellow fever vaccine YF17D on Day 30. |
| AS01 + YF17D at 3 Months | Experimental | Biological: AS01 adjuvant (0.5 mL intramuscular), Biological: YF17D (Stamaril, Sanofi-Pasteur)Participants receive AS01 (0.5 mL IM on Day 0) and yellow fever vaccine YF17D on Day 90. |
| Placebo + YF17D at 1 Month | Placebo comparator | Biological: YF17D (Stamaril, Sanofi-Pasteur), Other: Placebo (NaCl 09%, 0.5mL)Participants receive placebo (0.9% saline, 0.5 mL IM on Day 0) and yellow fever vaccine YF17D on Day 30. |
| Placebo + YF17D at 3 Months | Placebo comparator | Biological: YF17D (Stamaril, Sanofi-Pasteur), Other: Placebo (NaCl 09%, 0.5mL)Participants receive placebo (0.9% saline, 0.5 mL IM on Day 0) and yellow fever vaccine YF17D on Day 90. |
Who may qualify
- Ages
- 21 to 59 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult
Key inclusion criteria (7 listed)
- Adults aged 21 to 59 years of age at time of screening.
- BMI 18.5 - 27.5 kg / m2 (BMI values for Asian population according to MOH guideline NIH Consensus Conference).
- Satisfactory baseline medical assessment as assessed by physical examination and a stable health status. For subjects with underlying comorbidities, the conditions must be deemed stable by the investigators, and they must not have any hospitalisation relating to these conditions in the last 6 months.
- Voluntarily participate, understand and sign an informed consent form approved by the Ethical Review Board.
- Subjects who are willing to comply with the requirements of the study protocol and scheduled visits. These requirements include completion of the subject diary, return for follow-up visits. Subjects should also be willing to make themselves available for the duration of the study, with access to a consistent means of contact.
Key exclusion criteria (29 listed)
- Previous vaccination against yellow fever, dengue either with a registered product or from participation in a previous vaccine study.
- Previously received AS01-adjuvanted vaccines (e.g. Recombinant zoster vaccine, RTS,S/AS01, RSVPre-F3-AS01), either with a registered product or from participation in a previous vaccine study.
- Planned administration of a AS01-adjuvanted vaccine or yellow fever vaccine other than the study vaccine during the study.
- Subjects who have been unwell in the last 7 days prior to screening.
- History of documented yellow fever and / or dengue infection.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| AS01 adjuvant (0.5 mL intramuscular)The AS01 suspension contains 50 mcg/micrograms of 3-O-desacyl-4'monophosphoryl lipid A (MPL) and 50 mcg/micrograms of Quillaja Saponaria Molina, fraction 21 (QS21), licensed by GSK, available as a separate vial from the licensed Shingrix vaccine. | Biological | AS01 + YF17D at 1 Month, AS01 + YF17D at 3 Months |
| YF17D (Stamaril, Sanofi-Pasteur)Also: YF17D, yellow fever vaccineStamaril, the live-attenuated yellow fever vaccine, utilises the YF17D strain. Stamaril is supplied in the form of powder and solvent for suspension for injection in pre-filled syringe, Yellow fever vaccine (live). | Biological | AS01 + YF17D at 1 Month, AS01 + YF17D at 3 Months, Placebo + YF17D at 1 Month, Placebo + YF17D at 3 Months |
| Placebo (NaCl 09%, 0.5mL)Also: Placebo, Saline placebo, Saline injectionThe placebo will consist of 0.9% saline solution in equivalent volume. | Other | Placebo + YF17D at 1 Month, Placebo + YF17D at 3 Months |
Primary outcome
Host Immune Response
Time frame: Days 0, 7, 14, 28, 56, 84 (3 months)
Explorative evaluation of host immune response profile (cytokines, immune cell populations, gene expression, epigenetic modifications) induced by AS01 versus placebo, using panel of validated multi-omics assay tests, over a 3-month period.
3 secondary outcomes
Viraemia Levels
Time frame: 7 days following yellow fever vaccine administration
B Cell Response
Time frame: 30 days
T Cell Response
Time frame: 30 days
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 15 Jun 2026.
- Background: PubMed 32397218Mok DZL, Chan KR. The Effects of Pre-Existing Antibodies on Live-Attenuated Viral Vaccines. Viruses. 2020 May 8;12(5):520. doi: 10.3390/v12050520.
- Background: PubMed 33045466Yau C, Gan ES, Kwek SS, Tan HC, Ong EZ, Hamis NZ, Rivino L, Chan KR, Watanabe S, Vasudevan SG, Ooi EE. Live vaccine infection burden elicits adaptive humoral and cellular immunity required to prevent Zika virus infection. EBioMedicine. 2020 Nov;61:103028. doi: 10.1016/j.ebiom.2020.103028. Epub 2020 Oct 9.
- Background: PubMed 33516277Tan AT, Linster M, Tan CW, Le Bert N, Chia WN, Kunasegaran K, Zhuang Y, Tham CYL, Chia A, Smith GJD, Young B, Kalimuddin S, Low JGH, Lye D, Wang LF, Bertoletti A. Early induction of functional SARS-CoV-2-specific T cells associates with rapid viral clearance and mild disease in COVID-19 patients. Cell Rep. 2021 Feb 9;34(6):108728. doi: 10.1016/j.celrep.2021.108728. Epub 2021 Jan 21.
- Background: PubMed 33851143Kalimuddin S, Tham CYL, Qui M, de Alwis R, Sim JXY, Lim JME, Tan HC, Syenina A, Zhang SL, Le Bert N, Tan AT, Leong YS, Yee JX, Ong EZ, Ooi EE, Bertoletti A, Low JG. Early T cell and binding antibody responses are associated with COVID-19 RNA vaccine efficacy onset. Med. 2021 Jun 11;2(6):682-688.e4. doi: 10.1016/j.medj.2021.04.003. Epub 2021 Apr 8.
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- Individual participant dataSharing planned: Undecided
Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Candice Y.Y. Chan, MBChB, MRCP principal investigator
Singapore General Hospital
Amit Singhal, B.Sc., M.Sc., Ph.D. principal investigator
A*Star
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 2 study testing AS01 adjuvant (0.5 mL intramuscular) and YF17D (Stamaril, Sanofi-Pasteur) in people with Immune System Responses and Trained Immunity After AS01 Administration and Healthy Adult, run by Singapore General Hospital at 1 site in Singapore.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 7 inclusion and 29 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 15 Jun 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in Singapore. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 2 studies give the treatment to a larger group to see whether it has the intended effect and to keep checking safety.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Candice Y.Y. Chan, MBChB, MRCP (+6563213479, candice.chan.y.y@singhealth.com.sg), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Host Immune Response (time frame: Days 0, 7, 14, 28, 56, 84 (3 months)). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT07527247, which also lists 74 linked publications.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 15 Jun 2026.