This is an observational study that aims to determine the effectiveness of a tetravalent dengue vaccine (CYD-TDV) when given through a community-based immunization program against hospitalized and /or severe virologically confirmed dengue.

This is a matched case-control study. Cases will be children who are admitted with a clinical suspicion of dengue at the study hospitals and were eligible to have received the dengue vaccine during the mass immunization. The outcome of interest is hospitalized and/or severe virologically-confirmed dengue and the exposure is receipt of the dengue vaccine. Each case will be matched to two controls who were also eligible to have received the dengue vaccine and lives in the same area as the case. Cases and controls will be matched by age and sex.

Inclusion Criteria:

CASE-CONTROL STUDIES

• For a suspected case to be enrolled in the study, he/she should:

  • Provide signed informed consent and assent (as applicable)
  • Be within the age group eligible to receive the dengue vaccine at the time of mass vaccination (i.e. no condition that would have made him/her ineligible for dengue vaccination)
  • Be admitted in any of the participating hospitals for suspected dengue
  • Have ≤5 days history of fever.
  • For the case to be included in the analysis, the participant must meet all the inclusion criteria above plus have virologically-confirmed dengue infection by RT-PCR

• For controls to be recruited into the study, he/she should:

  • Provide signed informed consent and assent (as applicable)
  • Be age and sex-matched to the case
  • Be from the same community as the matched case
  • Be eligible to have received dengue vaccine during the community-based dengue immunization campaign in 2017 (i.e. no condition that would have made him/her ineligible for dengue vaccination)
  • Have had no episode of clinically-diagnosed or laboratory-confirmed dengue fever from the start of the community -based dengue immunization campaign to the focal time (the date of onset of dengue fever in the matched case)
  • Should not have been previously recruited as a control.

Exclusion Criteria:

• Any subject whose parent/guardian refuse to provide informed consent and/or assent.

• In addition, the following conditions automatically exclude children from the dengue mass immunization:

  • Children <9 years or adults older than 45 years of age
  • Anyone who is allergic or has had an allergic reaction to a prior dose or to any component of the dengue vaccine
  • Recipient of blood product in the last 3 months
  • Immunocompromised individuals, due to but not limited to genetic defects, HIV infection, or therapies that affect the immune system such as high-dose corticosteroids or chemotherapy
  • Recipient of any vaccine within the past month
  • History of bleeding disorder
  • Pregnant or breastfeeding women
  • Enrolled in dengue vaccine Phase 3 clinical study

Individuals to be enrolled in the study as probable cases will be admitted patients in the hospital study sites who are residents of the area, eligible to have received the dengue vaccine at the time of the initiation of community-based dengue vaccination program, and suspected to have dengue.