Trends in effectiveness of inactivated influenza vaccine in children by age groups in seven seasons immediately before the COVID-19 era

Masayoshi Shinjoh, Munehiro Furuichi, Hisato Kobayashi, Yoshio Yamaguchi, Naonori Maeda, Mizuki Yaginuma, Ken Kobayashi, Taisuke Nogayama, Michiko Chiga, Mio Oshima, Yuu Kuramochi, Go Yamada, Atsushi Narabayashi, Ichiro Ookawara, Mitsuhiro Nishida, Kenichiro Tsunematsu, Isamu Kamimaki, Motoko Shimoyamada, Makoto Yoshida, Akimichi ShibataYuji Nakata, Nobuhiko Taguchi, Keiko Mitamura, Takao Takahashi

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)


Background: We have reported the vaccine effectiveness of inactivated influenza vaccine in children aged 6 months to 15 years between the 2013/14 and 2018/19 seasons. Younger (6–11 months) and older (6–15 years old) children tended to have lower vaccine effectiveness. The purpose of this study is to investigate whether the recent vaccine can be recommended to all age groups. Methods: The overall adjusted vaccine effectiveness was assessed from the 2013/14 until the 2020/21 season using a test-negative case-control design based on rapid influenza diagnostic test results. Vaccine effectiveness was calculated by influenza type and by age group (6–11 months, 1–2, 3–5, 6–12, and 13–15 years old) with adjustments including influenza seasons. Results: A total of 29,400 children (9347, 4435, and 15,618 for influenza A and B, and test-negatives, respectively) were enrolled. The overall vaccine effectiveness against influenza A, A(H1N1)pdm09, and B was significant (44% [95% confidence interval (CI), 41–47], 63% [95 %CI, 51–72], and 37% [95 %CI, 32–42], respectively). The vaccine was significantly effective against influenza A and B, except among children 6 to 11 months against influenza B. The age group with the highest vaccine effectiveness was 1 to 2 years old with both influenza A and B (60% [95 %CI, 55–65] and 52% [95 %CI, 41–61], respectively). Analysis for the 2020/21 season was not performed because no cases were reported. Conclusions: This is the first report showing influenza vaccine effectiveness by age group in children for several seasons, including immediately before the coronavirus disease (COVID-19) era. The fact that significant vaccine effectiveness was observed in nearly every age group and every season shows that the recent vaccine can still be recommended to children for the upcoming influenza seasons, during and after the COVID-19 era.

Original languageEnglish
Pages (from-to)3018-3026
Number of pages9
Issue number22
Publication statusPublished - 2022 May 11


  • COVID-19 era
  • Children
  • Influenza
  • Test-negative design
  • Vaccine
  • Vaccine effectiveness

ASJC Scopus subject areas

  • Molecular Medicine
  • Immunology and Microbiology(all)
  • veterinary(all)
  • Public Health, Environmental and Occupational Health
  • Infectious Diseases


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