Impact of COVID-19 on the mental health of primary schoolchildren during the later phase of the pandemic: A case report of an 18-month longitudinal survey in a Japanese primary school.

Background: Drastic changes such as school closures and stay-at-home measures due to the global COVID-19 pandemic, may have long-term negative effects on children's mental health; however, longitudinal studies after 2021 are limited. This study aimed to observe the long-term effects of the COVID-19 pandemic on children's mental health by exploring changes in their mental health over a period of 18 months. Study design: We conducted a longitudinal study at Chiba Prefecture in Japan, focusing on schoolchildren's mental health changes. Methods: Data were obtained from the Strengths and Difficulties Questionnaire (SDQ) questionnaire conducted at single primary school three times from October 2021 to March 2023 which and included 183 participants. This study adopted a linear-mixed model to evaluate changes in children's SDQ scores, with sex and grade as the independent variables, and participants as a random effect. Results: Regarding changes in SDQ scores, there were no significant changes in the total difficulty scores or in each subscale; Emotional Symptoms, Conduct Problems, Hyperactivity/Inattention, Peer Problems, and Prosocial Behavior. There was no statistically significant interaction between changes in SDQ scores and sex. Conclusions: This report indicates that the impact of the COVID-19 pandemic on the mental health of Japanese primary schoolchildren was negligible in the later phase of the pandemic. However, the impact may differ from country to country owing to factors such as social restrictions during the COVID-19 pandemic.