Effectiveness of inactivated influenza vaccine in children during the 2023/24 season: The first season after relaxation of intensive COVID-19 measures.

BACKGROUND

The annual administration of the influenza vaccine is the most effective method for preventing influenza. We have evaluated the effectiveness of the inactivated influenza vaccine in children aged 6 months to 15 years across the seasons from 2013/2014 to 2022/2023. This study aims to investigate the effectiveness of the inactivated influenza vaccine in the 2023/2024 season, the first year following the easing of strict COVID-19 measures, and possibly the last season when only the inactivated vaccine is available on the market.

METHODS

Adjusted vaccine effectiveness for the 2023/2024 season was assessed using a test-negative case-control design, with results based on polymerase chain reaction and rapid influenza diagnostic tests. Vaccine effectiveness was calculated by influenza type and patient hospitalization/outpatient status.

RESULTS

A total of 1832 children were recruited. The inactivated influenza vaccine was effective in preventing both symptomatic influenza A and B in both inpatient and outpatient settings. Overall vaccine effectiveness for influenza A was 51% (95% confidence interval [CI], 23%-69%, n = 930) in inpatient settings and 54% (95%CI, 27%-71%, n = 559) in outpatient settings. For influenza B, effectiveness was 60% (95%CI, 22%-79%, n = 859) in inpatient settings and 56% (95%CI, 26%-74%, n = 558) in outpatient settings. Analysis suggested that administering two doses enhanced effectiveness specifically against influenza B.

CONCLUSIONS

This is the first study to demonstrate influenza vaccine effectiveness in children after the relaxation of strict COVID-19 measures in Japan (2023/2024). We recommend the current inactivated vaccine for preventing both influenza A and B in children, with consideration for the potential use of two doses to enhance effectiveness against influenza B.

Informations de copyright

Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.

Déclaration de conflit d'intérêts

Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Masayoshi Shinjoh (Shinjo) reports a relationship with MSD KK that includes: speaking and lecture fees. Masayoshi Shinjoh (Shinjo) reports a relationship with Meiji Seika Pharma Co Ltd. that includes: speaking and lecture fees. Masayoshi Shinjoh (Shinjo) reports a relationship with Mitsubishi Tanabe Pharma Corporation that includes: speaking and lecture fees. Masayoshi Shinjoh (Shinjo) reports a relationship with KM Biologics Co Ltd. that includes: speaking and lecture fees. Masayoshi Shinjoh (Shinjo) reports a relationship with Shionogi and Co Ltd. that includes: speaking and lecture fees. Masayoshi Shinjoh (Shinjo) reports a relationship with DAIICHI SANKYO COMPANY, LIMITED that includes: speaking and lecture fees. Masayoshi Shinjoh (Shinjo) reports a relationship with Takeda Pharmaceutical Company Limited that includes: consulting or advisory and speaking and lecture fees. Masayoshi Shinjoh (Shinjo) reports a relationship with Pfizer Japan Inc. that includes: consulting or advisory. Masayoshi Shinjoh (Shinjo) reports a relationship with Janssen Pharmaceutical KK that includes: consulting or advisory. Masayoshi Shinjoh (Shinjo) reports a relationship with Astellas Pharma Inc. that includes: consulting or advisory. This work was supported by JSPS KAKENHI, Japan (Grant Number JP20K10546). Outside this study, the corresponding author received Health Labour Sciences Research Grant, Japan (2024). If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.