Understanding immune responses to the Yellow Fever (YF) and Japanese Encephalitis (JE) flavivirus vaccines (The FLAVIFLAV Study)
The effect of the order of Japanese Encephalitis and Yellow Fever vaccine administration on Yellow Fever vaccine protection in healthy adults.
The University of Melbourne
88 participants
Oct 31, 2025
Interventional
Conditions
Summary
Japanese Encephalitis (JE) vaccine and Yellow Fever (YF) vaccine we are using in this study are both “attenuated” vaccines. This means the virus they contain is live but has been weakened and doesn’t cause sickness in healthy people. After JE or YF vaccination, the weakened virus can reproduce itself a little bit for around 1-2 weeks, this makes your immune system start fighting the weakened virus and gives you lasting protection against the disease. The JE vaccine virus has part of the YF virus inside it. If someone is having both vaccines, isn’t known if the order you receive the vaccines changes the immune response to the vaccine viruses. The primary study objective is to assess how the adaptive immune response (responses to antigen) to a live-attenuated JE vaccine impacts the replication of YF virus vaccine following YF vaccination. We will randomise participants to the order in which they receive a YF vaccine and a JE vaccine (JE-YF or YF-JE vaccination arms), given 4 months apart. Participants will have blood samples collected to follow their immune responses to the vaccines.
Eligibility
Inclusion Criteria10
- Healthy adults:
- Aged 18-60 years
- Healthy with no significant immunosuppressive illnesses. These include but are not limited to:
- cancer or treatment of cancer or organ transplantation
- treatment of auto-immune or inflammatory conditions such as inflammatory arthritis or inflammatory bowel disease
- use of corticosteroid, TNF inhibitor, interleukins, interferons, cyclosporine or other immunosuppressive medications
- significant renal or liver disease
- Willing and available to have blood samples taken per the schedule of events
- Willing to receive YF vaccine and JE vaccine
- Willing to be randomly assigned to receive the vaccines 4 month apart in different order (either JE-YF or YF-JE)
Exclusion Criteria13
- prior YF disease or vaccination
- prior JE disease or vaccination
- Symptomatic HIV infection or asymptomatic HIV with impaired immune function (CD4 T-cell count <200 cells/mm3
- history of thymus dysfunction (including myasthenia gravis, thymoma or thymectomy (for any reasons).
- a history of severe allergic reaction to eggs or chicken proteins
- Pregnant or breastfeeding women and women planning to become pregnant
- Unwilling to use reliable contraception around the timing of the vaccine (one month before and one month after)
- Receiving medication that might reduce immune responses. These include but are not limited to:
- systemic corticosteroids
- interleukins
- interferons
- cyclosporine
- systemic chemotherapy
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Interventions
Yellow Fever (YF) vaccine and Japanese Encephalitis (JE) vaccine. Participants will be randomised to the order in which they receive a YF vaccine and a JE vaccine (JE-YF or YF-JE vaccination arms), given 4 months apart. YF vaccine - 0.5 mL single dose of reconstituted vaccine given by intramuscular or subcutaneous injection. JE vaccine - 0.5 mL single dose of the reconstituted vaccine given by intramuscular injection to the deltoid region of the upper arm Adherence to vaccine order will be monitored by audit of case report files and REDCap
Locations(1)
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ACTRN12625000742471