COVID-19 pandemic and language development in children at 18 months in Japan

Abstract Background The COVID-19 pandemic has impacted public health globally. This study evaluates the pandemic's effects on language development in 18-month-old children in Japan, where strict control measures persisted longer. Methods This repeated cross-sectional study included 39,840 children attending 18-month health checkups conducted by the Okayama City Public Health Center (January 2017-March 2024). We compared language development before and during the pandemic, further dividing the pandemic into early (April 2020-March 2022) and late (April 2022-March 2024) periods. The primary outcome was the proportion of children requiring follow-up based on three language development questions. We defined the secondary outcome as the proportion of children who could not say three or more meaningful words. Risk ratios (RRs) and 95% CIs were estimated adjusting for confounders, with subgroup analyses by sex, childcare location (home, nursery school), and family size (≤3, ≥4). Results Compared with the pre-pandemic period, increased RRs were observed during the pandemic: 1.19 (95% CI, 1.15-1.22) for the primary outcome and 1.16 (95% CI, 1.11-1.22) for the secondary outcome. RRs were higher in the late than in the early period. Adverse impacts were more pronounced in girls than boys, in children cared for at home, and in those with smaller families. Conclusions The COVID-19 pandemic was associated with delayed language development in 18-month-old children, with more pronounced effects in the late pandemic period. This suggests that reduced social interaction may have affected language development, especially among children born after the pandemic onset who experienced prolonged exposure to pandemic-related factors. Moreover, subgroup analyses identified sociodemographic factors associated with children more vulnerable to pandemic effects. The findings highlight the need for strategies to prevent isolation and warrant long-term follow-up studies to evaluate developmental impacts. Key messages • The COVID-19 pandemic increased the risk of language impairment in 18-month-old children in Japan. • More extensive support is needed for higher-risk families, as well as follow-up of long-term development in children affected by the COVID-19 pandemic.