Inclusion Criteria:

Cohort:

To be eligible for inclusion in the study cohort, participants must meet the following inclusion criteria:

1. The participant is a child or adolescent eligible to be vaccinated with TDV as part of a vaccination program planned in the study area.
2. The participant's family do not intend to migrate away from the cohort hospital catchment area within 3 years of his/her enrollment into the study cohort.
3. The participant's parent(s) or legally acceptable representative (LAR) signs and dates a written informed consent form (ICF), and any required privacy authorization where applicable, prior to the initiation of any study procedures, after the nature of the study has been explained according to local regulatory requirements.
4. The participant signs and dates an age-appropriate assent form prior to the initiation of any study procedures, after the nature of the study has been explained according to local regulatory requirements.
5. The participant's parent(s) or LAR agrees that a baseline blood sample may be taken from the participant.

Cases:

To be eligible for inclusion as a case, participants must meet the following inclusion criteria:

1. The participant is part of the cohort.
2. The participant is hospitalized and clinically diagnosed with dengue.
3. The participant has a blood sample available that was taken preferably within 5 days of fever onset and/or onset of symptoms compatible with dengue.
4. The participant tested positive for dengue by RT-PCR.

Controls:

To be eligible for inclusion as a matched control, participants must meet the following inclusion criteria:

1. The participant is part of the cohort.
2. The participant had not been hospitalized with VCD at any point between enrollment in the cohort and the index date (that is, when his/her matched case was hospitalized with CDD).
3. The participant is a resident in the same neighbourhood as the matched case.
4. The participant's date of birth is in the same calendar year as the matched case.

Exclusion Criteria

Cases:

To be eligible for inclusion as a case participants must not meet any of the following criteria:

1. The participant has been vaccinated with TDV, a tetravalent, live attenuated, chimeric dengue vaccine in a yellow fever 17D backbone (CYD-TDV), or an investigational dengue vaccine prior to cohort enrollment.
2. Contraindications as per the locally approved label/product information leaflet.

Controls:

To be eligible for inclusion as a control participants must not meet any of the following criteria:

1. The participant has been vaccinated with TDV, CYD-TDV, or an investigational dengue vaccine prior to cohort enrollment.
2. Contraindications as per the locally approved label/product information leaflet.
3. The participant could not be contacted at the time of being selected as a control.