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Real-world effectiveness of influenza vaccination amongst children aged under 5 in a tropical setting

Liang En Wee1, Reen Wan Li Ho2, Jue Tao Lim3

  • 1Communicable Diseases Agency, Singapore; Duke-NUS Graduate Medical School, National University of Singapore, Singapore; Department of Infectious Diseases, Singapore General Hospital, Singapore; Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore.

The Journal of Infection
|May 27, 2026
PubMed

Insights

Influenza vaccination provides real-world protection for young children in tropical climates, but effectiveness wanes significantly over time. This study highlights the need for further research into optimal vaccination strategies in these regions.

Area of Science:

  • Pediatric Infectious Diseases
  • Vaccinology
  • Tropical Medicine

Background:

  • Limited data exists on influenza vaccine effectiveness in children residing in tropical regions with year-round influenza transmission.
  • Understanding vaccine performance in diverse epidemiological settings is crucial for public health strategies.

Purpose of the Study:

  • To evaluate the real-world effectiveness of influenza vaccination in Singaporean children under 5 years old.
  • To assess the waning of vaccine protection over time in this pediatric population.

Main Methods:

  • A population-based retrospective cohort study was conducted from May 2022 to April 2024.
  • Overlap-weighted Cox regression analyzed influenza hospitalization risk in vaccinated versus unvaccinated children.
  • Waning protection was assessed using logistic regression, comparing different time intervals post-vaccination.

Main Results:

  • Overall influenza vaccine effectiveness was 53% (95% CI: 44%-60%) in children under 5.
  • Relative vaccine effectiveness waned to 21% by 39-52 weeks post-vaccination.
  • In vaccine-naïve children, effectiveness declined to 11% after one dose and 13% after two doses by 39-52 weeks.

Conclusions:

  • Influenza vaccination offers protection to young children in tropical settings, but this protection diminishes rapidly.
  • The benefit of a two-dose primary vaccination series may be less pronounced in tropical regions compared to temperate zones.
Abstract

Keywords:
ChildrenInfluenzaTropicalVaccinationVaccine-effectivenessWaning

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