Official title: Immunogenicity of an intradermal Qdenga vaccine among healthy volunteers: A pilot study

As in the setting of low- to middle-income countries, to demonstrating that lower doses of vaccine via intradermal route can still elicit robust immune responses, thereby lowering the overall cost of vaccination might be particularly meaningful ,with possible extra benefit of experiencing fewer side effects or risk of allergy. This study goal is to explores the potential of intradermal administration of Qdenga, hypothesizing that a lower dose via this route could achieve adequate immunogenicity compared to the standard subcutaneous administration, thus offering a cost-effective alternative particularly in low-resource settings where dengue is most prevalent.

Inclusion Criteria:

• Thai adult aged 18-60 years, who not previously received dengue vaccine.
• The subjects are able to and willing to comply with the requirements of the clinical trial program and could complete the 3-month follow-up of the study.
• Individuals who are in good health condition at the time of entry into the trial as determined by medical history, physical examination and clinical judgment of the investigator and meet the requirements of immunization
• The subject can provide with informed consent and sign informed consent form

Exclusion Criteria:

• Have a medical history or family history of convulsion, epilepsy, encephalopathy and psychosis.
• Be allergic to any component of the research vaccines or used to have a history of hypersensitivity or serious reactions to vaccination.
• Women with positive urine pregnancy test, pregnant or breast-feeding, or have a pregnancy plan within six months.
• Have acute infectious diseases, including dengue infection
• Have severe chronic diseases or condition in progress cannot be controlled. For example, poor controlled DM and uncontrolled HT.
• Have the history of urticaria 1 year before receiving the investigational vaccine.
• Have known underlying diseases of thrombocytopenia or other coagulation disorders (which may cause contraindications for intramuscular injection).
• Have needle sickness.
• Have the history of immunosuppressive therapy, cytotoxic therapy or systemic corticosteroids
• Have received blood products within 4 months before injection of investigational vaccines.
• Under anti-tuberculosis treatment.
• Not be able to follow the protocol, or not be able to understand the informed consent according to the researcher's judgment, due to various medical, psychological, social or other conditions.

The data will be anonymized.

Day 37, 60 (7 and 30 days post 1st vaccination) and Day 97, 120 (7 and 30 days post 2nd vaccination)

This pilot study is limited by small sample size, short follow-up, and lack of neutralization assays and detailed T-cell phenotyping. These factors restrict interpretation of durability, serotype-specific responses, and immune correlates. Larger studies with extended immunologic assessments are planned.