Ho Geol Woo, MD, PhD1; Sangil Park, MD1; Hyunju Yon, MD2; Seung Won Lee, MD, PhD3; Ai Koyanagi, MD, PhD4,5; Louis Jacob, PhD4,6; Lee Smith, PhD7; Wonyoung Cho, PhD8; Chanyang Min, PhD8; Jinseok Lee, PhD9; Hayeon Lee, MS9; Rosie Kwon, MS8,10; Guillaume Fond, PhD11,12; Laurent Boyer, PhD11,12; Yoonie Yoonjung Joo, PhD13; Yong Sung Choi, MD, PhD14; Seung-Geun Yeo, MD, PhD15; Sang Youl Rhee, MD, PhD8,16; Jae Il Shin, MD, PhD17; Dong Keon Yon, MD8,14

1Department of Neurology, Kyung Hee University Medical Center, Kyung Hee University College of Medicine, Seoul, South Korea
2Department of Medicine, Kyung Hee University College of Medicine, Seoul, South Korea
3Department of Precision Medicine, Sungkyunkwan University School of Medicine, Suwon, South Korea
4Research and Development Unit, Parc Sanitari Sant Joan de Deu, Network Centre for Biomedical Research in Mental Health, Health Institute Carlos III, Barcelona, Spain
5Catalan Institution for Research and Advanced Studies (ICREA), Pg. Lluis Companys, Barcelona, Spain
6Faculty of Medicine, University of Versailles Saint-Quentin-en-Yvelines, Montigny-le-Bretonneux, France
7Centre for Health, Performance and Wellbeing, Anglia Ruskin University, Cambridge, United Kingdom
8Center for Digital Health, Medical Science Research Institute, Kyung Hee University College of Medicine, Seoul, South Korea
9Department of Biomedical Engineering, Kyung Hee University, Yongin, South Korea
10Department of Biomedical Engineering, University of Michigan, Ann Arbor
11Assistance Publique-Hôpitaux de Marseille, Aix-Marseille University, CEReSS–Health Service Research and Quality of Life Center, Marseille, France
12Depression and Schizophrenia Expert Center, FondaMental Foundation, Creteil, France
13Institute of Data Science, Korea University, Seoul, South Korea
14Department of Pediatrics, Kyung Hee University Medical Center, Kyung Hee University College of Medicine, Seoul, South Korea
15Department of Otolaryngology–Head & Neck Surgery, Kyung Hee University Medical Center, Kyung Hee University College of Medicine, Seoul, South Korea
16Department of Endocrinology and Metabolism, Kyung Hee University School of Medicine, Seoul, South Korea
17Department of Pediatrics, Yonsei University College of Medicine, Seoul, South Korea

Drs Woo, Park, and H. Yon contributed equally to this work.
Corresponding Authors: Jae Il Shin, MD, PhD, Dong Keon Yon, MD

Importance: Despite the COVID-19 pandemic's effect on daily life, limited research exists on the prevalence and risk factors of suicidality and sadness among South Korean adolescents.

Objectives: To examine whether the observed sadness and suicidality in the early to middle periods of the COVID-19 pandemic differed from the expected level and to investigate changes in risk factors for sadness and suicidality.

Design, setting, and participants: This nationwide serial cross-sectional survey study used data on 1 109 776 Korean adolescents aged 13 to 18 years from the Korea Youth Risk Behavior Web-based Survey from 2005 to 2021.

Exposure: The COVID-19 pandemic.

Main outcomes and measures: The pattern of changes in the percentage or proportion of sadness or suicidality, as well as the risk factors for sadness or suicidality. The transitional effect of the COVID-19 pandemic was assessed using weighted odds ratios (wORs) or weighted beta coefficients with 95% CIs.

Results: Between 2005 and 2021, 1 109 776 adolescents (mean [SD] age, 15.0 [1.7] years; 51.5% male adolescents; and 51.7% in grades 7-9 and 48.3% in grades 10-12) were included in the Korea Youth Risk Behavior Web-based Survey. The slope of the long-term trends in sadness and suicidality decreased in the prepandemic period (sadness: from 37.8% [95% CI, 37.4%-38.2%] in 2005-2007 to 26.1% [95% CI, 25.9%-26.4%] in 2016-2019; suicidality: from 23.0% [95% CI, 22.7%-23.3%] in 2005-2007 to 12.3% [95% CI, 12.1%-12.5%] in 2016-2019), whereas the slope increased during the COVID-19 pandemic (sadness: from 25.0% [95% CI, 24.5%-25.6%] in 2020 to 26.6% [95% CI, 26.1%-27.1%] in 2021; trend difference in β, 0.249 [95% CI, 0.236-0.262]; suicidality: from 10.7% [95% CI, 10.3%-11.1%] in 2020 to 12.5% [95% CI, 12.1%-12.9%] in 2021; trend difference in β, 0.328 [95% CI, 0.312-0.344]). The trends presented a similar tendency in the subgroups according to sex, school grade, residential area, smoking status, and current alcohol use. Compared with the prepandemic period, the risk factors associated with sadness during the pandemic were younger age (wOR, 0.907; 95% CI, 0.881-0.933), female sex (wOR, 1.031; 95% CI, 1.001-1.062), urban residence (wOR, 1.120; 95% CI, 1.087-1.153), current smoking status (wOR, 1.134; 95% CI, 1.059-1.216), and current alcohol use (wOR, 1.051; 95% CI, 1.002-1.102). Female sex (wOR, 1.064; 95% CI, 1.021-1.109), urban residence (wOR, 1.117; 95% CI, 1.074-1.162), and low economic status (wOR, 1.286; 95% CI, 1.180-1.403) were the risk factors significantly associated with suicidality after the COVID-19 pandemic began.

Conclusions and relevance: In this nationwide serial cross-sectional survey study of South Korean adolescents, the slope of the prevalence of sadness and suicidality increased during the COVID-19 pandemic after a decrease prior to the pandemic. The findings suggest that public health measures are needed to recognize vulnerable groups with risk factors and to prevent an increase in sadness and suicidality among adolescents during the COVID-19 pandemic.