J Korean Med Sci.  2021 Mar;36(10):e71. 10.3346/jkms.2021.36.e71.

Influenza Vaccine Effectiveness in Children at the Emergency Department during the 2018-2019 Season: the First Season School-aged Children Were Included in the Korean Influenza National Immunization Program

• Yoon Y
• Choi Js
• Park M
• Cho H
• Park M
• Huh HJ
• Kim YJ
• Son MH

• KMID: 2513708
• DOI: http://doi.org/10.3346/jkms.2021.36.e71

Abstract

Background
For the 2018–2019 season, the national influenza immunization program expanded to cover children aged from 6 months to 12 years in Korea. This study aimed to analyze vaccine effectiveness (VE) against influenza in children visiting the pediatric emergency room at a tertiary hospital during the 2018-2019 season.
Methods
Patients tested for influenza antigens from October 1st 2018 to May 31st 2019 at the pediatric emergency room of Samsung Medical Center were included. Patients' influenza antigen test results, influenza vaccination history, and underlying medical conditions were reviewed retrospectively. VE was estimated from the test-negative design study.
Results
Among the 2,901 visits with influenza test results 1,692 visits of 1,417 patients were included for analysis. Among these 1,417 patients, 285 (20.1%) were positive (influenza A, n = 211, 74.0%; influenza B, n = 74, 26.0%). The VE in all patients was 36.4% (95% confidence interval [CI], 13.9 to 53.1). The VE for influenza A was 37.6% (95% CI, 12.6 to 55.5) and VE for influenza B was 24.0% (−38.5 to 58.3). The VE in the age group 6 months to 12 years was significant with a value of 35.6% (95% CI, 10.5 to 53.7); it was not statistically significant in the age group 13 to 18 years. In a multivariate logistic regression model, patients who received an influenza vaccination were less likely to get influenza infection (OR, 0.6; 95% CI, 0.4 to 0.8; P = 0.001), with significant confounding factors such as age group 13 to 18 years (OR, 0.5; 95% CI, 0.3 to 0.8; P = 0.003) and underlying hematology-oncology disease (OR, 0.3; 95% CI, 0.1 to 0.6; P = 0.002).
Conclusion
We report moderate effectiveness of influenza vaccination in previously healthy children aged from 6 months to 12 years in the 2018-2019 season.

Keyword

Influenza; Vaccine Effectiveness; Children; National Immunization Program

Figure

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  Fig. 1 Study flow chart.ER = emergency room, Ag = antigen.

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  Fig. 2 Number of test-positive results according to influenza type.

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  Fig. 3 Number of specimens positive for influenza. Data is arranged according to influenza type, subtype, and surveillance week for the 2018-2019 season in (A) Republic of Korea, (B) Japan, (C) United States and (D) Australia (WHO data).

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