Primary objectives:

• To assess how dengue vaccine efficacy varies across participant subgroups regarding polymorphism in human leukocyte antigen (HLA) alleles of interest.
• To assess the association between HLA alleles and, serotype-specific neutralization antibody titers and summary neutralization measure in the vaccine and placebo groups.
• To assess the association between the polymorphism in HLA alleles of interest and susceptibility to Dengue fever and Dengue Haemorrhagic fever.

Secondary objectives:

• To assess whether dengue serotype-specific neutralizing antibody titers and associated summary neutralization measure at 28 days post-dose 3 are related to the rate of occurrence of symptomatic Virologically-confirmed dengue infection after post-dose 3
• To evaluate whether the dengue serotype-specific neutralizing antibody and associated summary neutralization measure at 28 days post-dose 3 are related to the level of vaccine efficacy against dengue viruses after post-dose 3.

The enrolled population will include both, virologically-confirmed (VC) dengue cases and subjects not having experienced a VC dengue infection (control subjects) from the first Proof of Concept efficacy study conducted in Thailand Analyses for correlates will be performed on samples collected in the context of the first proof of concept efficacy study. Sequencing of dengue viruses will also be done on samples collected within the same context. Immunogenetic testing will be performed on saliva samples collected at the study enrollment visit.

No intervention or vaccine will be provided or administered as part of this study.

Inclusion Criteria:

• Subject currently enrolled in, or having recently finished, CYD57 (NCT01983553; long-term safety follow-up study of the first PoC efficacy study), included in the subjects list provided by the Sponsor, with or without past experience of virologically confirmed dengue.
• For children 7 to < 18 years. Assent form (AF) has been signed and dated by the subject, and informed consent form (ICF) has been signed and dated by the parents or another legally acceptable representative and by independent witness, as per local Ethics Committee (EC) requirement. For subjects ≥ 18 years. ICF has been signed and dated by the subject and by independent witness, as per local EC requirement.
• Subject (and parent(s) / legally acceptable representative for subject < 18 years) are able to attend the scheduled visit and can comply with all study procedures.

Exclusion Criteria:

• Any illness that, in the opinion of the Investigator, might interfere with study procedures.

Participants will include both, virologically-confirmed (VC) dengue cases and subjects not having experienced a VC dengue infection (control subjects) from the first Proof of Concept efficacy study CYD57 (NCT01983553) conducted in Thailand

Qualified researchers may request access to patient level data and related study documents including the clinical study report, study protocol with any amendments, blank case report form, statistical analysis plan, and dataset specifications. Patient level data will be anonymized and study documents will be redacted to protect the privacy of trial participants. Further details on Sanofi's data sharing criteria, eligible studies, and process for requesting access can be found at: https://vivli.org