Article in Japanese

Three doses of BNT162b2 vaccine against the SARS-CoV-2 Omicron subvariant in preventing the onset of COVID-19 in children aged 5 to 11 years

Ryuta Terao^1）, Fujio Kakuya^1）, Hitoshi Okubo^1）, Hiroaki Fujiyasu^1）, Fumie Inyaku^1）, Takahiro Kinebuchi^2）

Background: In July 2022, the Omicron subvariants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV2) changed from BA.2 to BA.5 in Japan. How effective three doses of the BNT162b2 vaccine are in preventing BA.5 subvariants in children aged 5–11 years in Japan had not been explored. Therefore, the clinical data of children from Furano City, Japan, were analyzed prospectively in order to evaluate the effectiveness of three doses of original BNT162b2 vaccine in preventing coronavirus disease 2019 (COVID-19) and compare it with two doses of BNT152b2, as reported in a previous study by these authors.
Methods: Children aged 5–11 years, who had received the third dose of BNT162b2 vaccine (vaccinated) from October to December 2022, were included in this study together with those who had never received it, but instead took the influenza or Japanese encephalitis vaccine (unvaccinated). The outcome was defined as COVID-19 onset within 180 days of vaccination.
Results: A total of 299 children were included in this study. The overall adjusted hazard ratio (HR) was 0.40 (0.25–0.63), indicating a significant difference in the effectiveness of COVID-19 prevention. Significant differences were observed in each group of 5–6-year-olds and 7–8-year-olds [HR: 0.36 (0.14–0.91) and 0.22 (0.11–0.46), respectively].
Conclusion: Three doses of BNT162b2 vaccine showed statically significant effectiveness against the SARS-CoV-2 Omicron subvariant. Three doses were more effective than two in children aged 5 to 11 years In Japan.

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1）Department of Pediatrics, Furano Kyokai Hospital, Furano, Japan
2）Department of Clinical Laboratory, Furano Kyokai Hospital, Furano, Japan

Key words	COVID-19, epidemiology, pandemic, SARS-CoV-2, vaccine
Received	October 10, 2024
Accepted	March 23, 2025

37 (2)：155─163,2025