Epidemiology and Health

Original articles

Health literacy in Korea: findings from the 2023 Korea National Health and Nutrition Examination Survey: Sunhye Choi, Yukyeong Kang, Hyejin Kim, Kyungwon Oh; Epidemiol Health. 2025;e2025037. Published online July 9, 2025; DOI: https://doi.org/10.4178/epih.e2025037 [Accepted]

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OBJECTIVES
This study aimed to assess health literacy and identify vulnerable groups, providing a basis for developing health policies aimed at improving health literacy, using data from the 2023 Korea National Health and Nutrition Examination Survey (KNHANES).
METHODS
The health literacy measurement tool used in the 2023 KNHANES comprised a total of 10 items spanning the domains of disease prevention, health promotion, healthcare, and technology and resources. Health literacy was analyzed in relation to sociodemographic characteristics and major health behaviors among 5,906 adults aged 19 years or older, using the SAS program.
RESULTS
As of 2023, the overall prevalence of adequate health literacy among adults was 60.4%. Adequate health literacy was higher in women (62.2%) than in men (58.6%). Younger individuals exhibited higher levels of health literacy, with those aged 19–64 years at 65.9%, compared to only 40.3% among those aged 65 or older. Higher income and education levels were also associated with greater health literacy. Regarding health behavior characteristics, individuals practicing healthy lifestyles, such as non-smoking, engaging in physical activity, and undergoing health checkups, demonstrated higher health literacy than those who did not engage in such behaviors.
CONCLUSIONS
Six out of 10 Korean adults demonstrated adequate health literacy, but significant differences were observed according to sociodemographic characteristics (e.g., age and education) and health behaviors (e.g., smoking and physical activity). Tailored education and policy initiatives are necessary to improve health literacy, particularly targeting older adults, low-income groups, individuals with lower education, and those who do not practice healthy lifestyles.; Summary

Associations of self-rated health, depression, and work ability with employee control over working time: Heejoo Ko, Seong-Sik Cho, Jaesung Choi, Mo-Yeol Kang; Epidemiol Health. 2025;e2025036. Published online July 8, 2025; DOI: https://doi.org/10.4178/epih.e2025036 [Accepted]

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OBJECTIVES
Work-time control (WTC), defined as employees’ ability to influence their work schedules, is a crucial determinant of work-life balance and well-being. This study aims to evaluate the associations between WTC and health-related outcomes among Korean workers and examine potential effect modifications by working hours and shift work status.
METHODS
This study analyzed data from the 2024 wave of the Korean Work, Sleep, and Health Study, a nationwide panel study of workers aged 19 to 70 years (n=5,195). WTC was measured using a 6-item scale, and participants were categorized into low (≤12) or high (>12) WTC groups. Outcomes included self-rated health (SRH), depression (measured by the Patient Health Questionnaire-9), and work ability (WA, measured by the Work Ability Index). Logistic regression models were used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for poor SRH, moderate-to-severe depression, and poor WA, adjusting for demographic and occupational variables. Subgroup analyses assessed effect modifications by working hours and shift work.
RESULTS
Higher WTC was associated with lower odds of poor SRH (OR, 0.730; 95% CI, 0.618 to 0.863), moderate-to-severe depression (OR, 0.710; 95% CI, 0.606 to 0.833), and poor WA (OR, 0.624; 95% CI, 0.463 to 0.841). These associations were significant among daytime workers but not shift workers. The protective effects of WTC were attenuated among workers exceeding 52 hours/week.
CONCLUSIONS
Higher WTC is associated with better health and work outcomes, emphasizing its importance for employee well-being. However, its benefits may be limited among shift workers and employees working excessive hours.; Summary

Occurrence rate and estimated economic burden of pulp and periapical disease treatment among Korean older adults: a national population-based retrospective study: Hyeonjeong Go, Masae Kuboniwa, Youn-Hee Choi; Epidemiol Health. 2025;e2025035. Published online July 3, 2025; DOI: https://doi.org/10.4178/epih.e2025035 [Accepted]

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Abstract PDF: Abstract
OBJECTIVES
Maintaining healthy dentition is essential for the overall health of older adults. Treatment of pulp and periapical disease (PPD) is crucial for preserving teeth. This study assessed the occurrence rate and economic burden of PPD treatment in an older Korean population.
METHODS
Data were obtained for adults aged ≥ 65 years from the Korean National Health Insurance Services from 2014 to 2018. The occurrence rate was defined as the proportion of individuals who received ≥1 PPD treatment. The economic burden was estimated using both direct and indirect expenditures, calculated from a societal perspective. Regression analysis was performed to evaluate yearly trends in occurrence rate and economic burden.
RESULTS
Direct costs, which included insured and non-insured medical expenses, ranged from $13.79 to $10.47 million. Indirect costs, comprising transportation and time costs, ranged from $0.89 to $0.80 million. Total costs declined from $14.68 to $11.36 million. The occurrence rate of PPD treatment decreased significantly from 1.24% to 0.91% (p<0.05). The economic burden also demonstrated a statistically significant downward trend, with total PPD costs decreasing from 0.00099% to 0.00066% of Korea's GDP, and from 0.63% to 0.30% of the annual total dental care benefit costs between 2014 and 2018 (p<0.05).
CONCLUSIONS
The occurrence rate and estimated economic burden of PPD treatment significantly decreased among older Korean adults from 2014 to 2018. Conservative approaches to tooth preservation contribute to more effective oral health policies and help reduce the economic burden of oral disease treatments in an aging society.; Summary

Identifying adverse reactions following COVID-19 vaccination from data collected through active surveillance: a text mining approach: Hye Ah Lee, Bomi Park, Chung Ho Kim, Yeonjae Kim, Hyunjin Park, Seunghee Jun, Hyelim Lee, Seunghyun Lewis Kwon, Yesul Heo, Hyungmin Lee, Hyesook Park; Epidemiol Health. 2025;e2025034. Published online June 30, 2025; DOI: https://doi.org/10.4178/epih.e2025034 [Accepted]

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OBJECTIVES
Unstructured text data collected through vaccine safety surveillance systems can identify previously unreported adverse reactions and provide critical information to enhance these systems. This study explored adverse reactions using text data collected through an active surveillance system following COVID-19 vaccination.
METHODS
We performed text mining on 2,608 and 2,054 records from 2 survey seasons (2023–2024 and 2024–2025), in which participants reported health conditions experienced within 7 days of vaccination using free-text responses. Frequency analysis was conducted to identify key terms, followed by subgroup analyses by sex, age, and concomitant influenza vaccination. In addition, semantic network analysis was used to examine terms reported together.
RESULTS
The analysis identified several common (≥1%) adverse events, such as respiratory symptoms, sleep disturbances, lumbago, and indigestion, which had not been frequently noted in prior literature. Moreover, less frequent (≥0.1% to <1%) adverse reactions affecting the eyes, ears, and oral cavity were also detected. These adverse reactions did not differ significantly in frequency based on the presence or absence of simultaneous influenza vaccination. Co-occurrence analysis and estimation of correlation coefficients further revealed associations between frequently co-reported symptoms.
CONCLUSIONS
This study utilized text mining to uncover previously unrecognized adverse reactions associated with COVID-19 vaccination, thereby broadening our understanding of the vaccine’s safety profile. The insights obtained may inform future investigations into vaccine-related adverse reactions and improve the processing of text data in surveillance systems.; Summary

Cohort profile

Cohort profile: Cardiovascular Metabolic Etiological Research Center COVID-19 Mental Health Survey (CC-MHS): Sun Jae Jung, Dongkyu Lee, Ji Su Yang, Sunghyuk Kang, Hyejin Kim, Jeong Hyun Ahn, Yunseong Heo, Jieun Noh, Changhyun Kim, Hyeon Chang Kim; Epidemiol Health. 2025;e2025033. Published online June 30, 2025; DOI: https://doi.org/10.4178/epih.e2025033 [Accepted]

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Abstract PDF: Abstract
The Cardiovascular Metabolic Etiological Research Center COVID-19 Mental Health Survey (CC-MHS) is a comprehensive longitudinal cohort study investigating the mental health impact of the COVID-19 pandemic by utilizing pre-existing baseline data from the CMERC cohort (2013–2018). This study assesses physical health, lifestyle changes, and mental health using validated tools, including the Patient Health Questionnaire-9 (PHQ-9), Generalized Anxiety Disorder-7 (GAD-7), and the PTSD Checklist for DSM-5 (PCL-5), and evaluates a population of urban and suburban South Korean participants across multiple dimensions. Through online surveys, the research identified gender-specific social support mechanisms, showing that men benefit from larger social networks, whereas women derive protective effects from stronger emotional connections. Key findings underscore complex interactions among demographic factors, psychological variables, and public health responses, especially in the context of vaccination attitudes and trust in pandemic management. The CC-MHS delivers critical insights into mental health trajectories during global health crises, offering valuable evidence for developing adaptive public health strategies and for understanding the intricate relationships between individual psychological resilience and broader societal health challenges.; Summary

Original articles

Being trans in South Korea: key milestones and stigmatization across life stages in a nationwide survey of 585 transgender and nonbinary young adults: Sungsub Choo, Ranyeong Kim, Hyemin Lee, Horim Yi, Rockli Kim, Seung-Sup Kim; Epidemiol Health. 2025;e2025032. Published online June 27, 2025; DOI: https://doi.org/10.4178/epih.e2025032 [Accepted]

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OBJECTIVES
Understanding the experiences of transgender and nonbinary (TGNB) individuals from a life-course perspective is essential. This article aims to identify ages at key milestones related to transgender identity and assess experiences of stigmatization among TGNB individuals across different life stages.
METHODS
We analyzed data from a nationwide longitudinal survey of 585 TGNB adults in South Korea collected in 2020 and 2021. Analysis of variance and chi-square test were used to compare mean ages at transgender identity developmental milestones and experiences of anti-transgender stigma across transgender identities.
RESULTS
On average, TGNB Koreans realized their transgender identity at age 13, accepted it at age 20, and came out to others at age 21. Regarding experiences of stigmatization across different life stages, 67.4% reported hearing homophobic and transphobic remarks from teachers in secondary school. Among TGNB individuals assigned male at birth (AMAB) who served mandatory military service, 29.0% were classified as maladjusted soldiers, and 12.1% experienced sexual harassment or violence. When asked about the job application process, 57.0% reported discontinuing their job search due to their transgender identity. Financial burden represented the primary barrier to psychiatric evaluations, hormone treatment, and gender-affirming surgery.
CONCLUSIONS
Our study identifies key milestone ages related to transgender identity and experiences of stigmatization across life stages among TGNB adults in South Korea. With 97.6% of participants under 40 years old, these findings primarily reflect the experiences of TGNB young adults. Further research is necessary to better understand the experiences of middle-aged and elderly TGNB individuals in South Korea.; Summary

Socioeconomic inequality in organized and opportunistic screening for breast cancer: results from the Korean National Cancer Screening Survey, 2009-2021: Yejin Ha, Xuan Quy Luu, Woorim Kim, Jae Kwan Jun, Mina Suh, Kui Son Choi; Epidemiol Health. 2025;e2025031. Published online May 30, 2025; DOI: https://doi.org/10.4178/epih.e2025031 [Accepted]

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Abstract PDF: Abstract
OBJECTIVES
Breast cancer screening rates have increased since the introduction of the National Cancer Screening Program (NCSP) in Korea. However, it remains unclear whether socioeconomic inequalities have improved, particularly according to screening type. This study investigated inequalities in organized (government-led) and opportunistic (individually initiated) screening, stratified by education and income levels.
METHODS
Data were obtained from the Korean National Cancer Screening Survey, conducted annually from 2009 to 2021, involving approximately 1,700 women each year except in 2009. Trends were analyzed using joinpoint regression to calculate average annual percent changes (AAPCs). Socioeconomic inequalities were assessed using the slope index of inequality (SII) and relative index of inequality (RII).
RESULTS
Organized screening rates increased from 42.0% in 2009 to 60.2% in 2021 (AAPC, 1.9; 95% confidence interval [CI], 0.7-3.4), whereas opportunistic screening rates declined from 13.3% to 11.2% (AAPC, -5.4; 95% CI, -8.7 to -2.3). For organized screening, individuals with lower education levels exhibited higher participation, resulting in negative inequality indices (SII, -5.37%; RII, 0.80). No significant income-based inequality was found (SII, 1.60; RII, 1.07). However, opportunistic screening demonstrated significant inequalities by both education (SII, 5.37%; RII, 1.92) and income (SII, 5.90%; RII, 1.96), with higher participation rates among more advantaged groups.
CONCLUSIONS
The NCSP has improved breast cancer screening rates and reduced income-related inequality in organized screening. However, educational and income-based inequalities persist in opportunistic screening. To reduce screening inequities, policy efforts are needed to further promote the NCSP, including improving program quality and providing financial support for follow-up examinations.; Summary

Spatial patterns of laboratory-confirmed leptospirosis in northeastern Peninsular Malaysia, 2016–2023: Hazlienor Mohd Hatta, Kamarul Imran Musa, Nik Mohd Hafiz Mohd Fuzi, Paula Moraga; Epidemiol Health. 2025;e2025030. Published online May 29, 2025; DOI: https://doi.org/10.4178/epih.e2025030 [Accepted]

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Abstract PDF: Abstract
OBJECTIVES
Leptospirosis presents significant public health challenges in endemic regions such as north-eastern Peninsular Malaysia. Spatial analysis is essential for visualising disease incidence and distribution, assessing vulnerability based on geographical and socio-economic factors, and ultimately informing targeted interventions, optimising resource allocation, and enhancing surveillance strategies. This study aimed to determine the incidence and characterise the spatial distribution of leptospirosis in Kelantan, Malaysia.
METHODS
All laboratory-confirmed leptospirosis cases reported in Kelantan between 2016 and 2023 were extracted from the Communicable Disease Control Information System (CDCIS) e-Notifikasi online database. Spatial analyses were performed using the spatstat, spdep, and ggplot2 packages within the RStudio integrated development environment.
RESULTS
The analysis encompassed 1534 laboratory-confirmed leptospirosis cases. The average crude annual incidence of leptospirosis cases per 1000 population from 2016 to 2023 was 0.101 (95% CI: 0.038, 0.164). Incidence varied considerably across districts and subdistricts, initially higher in the north but declining over time, while consistently high and increasing incidence was observed in the southern region. Significant clustering of leptospirosis cases occurred throughout the studied years, except during the COVID-19 pandemic. Hotspots were initially prevalent in northern areas but later emerged in south-eastern and southern regions. Significant spatial autocorrelation evolved from high-low to high-high clusters, particularly evident in central and southern regions.
CONCLUSIONS
This study provides valuable local epidemiological and spatial insights into the endemicity of leptospirosis. The findings highlight the need for targeted interventions and continued surveillance to effectively mitigate the leptospirosis burden in endemic areas.; Summary

Safety of combination therapy of azilsartan medoxomil and amlodipine: a population-based cohort study: Hyesung Lee, Bin Hong, Chris Tzu-Ting Su, Sungho Bea, Han Eol Jeong, Kyungyeon Jung, Michael Chun-Yuan Cheng, Zoe Chi-Jui Chang, Edward Chia-Cheng Lai, Jongyoung Lee; Epidemiol Health. 2025;e2025029. Published online May 28, 2025; DOI: https://doi.org/10.4178/epih.e2025029 [Accepted]

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Abstract PDF: Abstract
OBJECTIVES
This study investigated the safety of azilsartan and amlodipine combination therapy versus other angiotensin receptor blockers (ARBs) and amlodipine in patients with hypertension.
METHODS
We conducted a cohort study utilizing healthcare databases from South Korea and Taiwan. Patients aged between 18 and 75 years who were newly prescribed both an ARB and amlodipine within 6 months of hypertension diagnosis were included. Safety outcomes assessed were hypotension, angioedema, acute pancreatitis, hyperkalemia, hypokalemia, toxic liver disease, hepatic failure, nausea and vomiting, and fall-related injury. Hazard ratios (HRs) with 95% confidence intervals (CIs) for each safety outcome associated with azilsartan medoxomil and amlodipine versus other ARBs combined with amlodipine were calculated within a 1:1 propensity score (PS)-matched cohort. Summary HRs across databases were computed using random-effects meta-analysis.
RESULTS
We identified 2,472 eligible patients (1,521 from Korea, 951 from Taiwan) initiating treatment with azilsartan medoxomil and amlodipine, and 671,468 patients (312,322 from Korea, 355,409 from Taiwan) initiating other ARBs with amlodipine. After PS matching, baseline characteristics were well-balanced between treatment groups. During the 180-day follow-up, most adverse outcomes did not occur even once in either group, thus precluding the calculation of HRs. The risk of acute pancreatitis was not significantly different between the azilsartan medoxomil and amlodipine group and the other ARB and amlodipine groups (summary HR, 0.86 [95% CI, 0.14–5.37]).
CONCLUSIONS
In this population-based cohort study, azilsartan medoxomil combined with amlodipine was not associated with an increased risk of adverse outcomes compared to other ARBs combined with amlodipine.; Summary

Mortality burden attributable to long-term exposure to fine particulate matter among older adults in South Korea: Jongmin Oh, Jisun Myung, Changwoo Han, Hyun Joo Bae, Soontae Kim, Yun-Chul Hong, Dong-Wook Lee, Youn-Hee Lim; Epidemiol Health. 2025;e2025028. Published online May 28, 2025; DOI: https://doi.org/10.4178/epih.e2025028 [Accepted]

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Abstract PDF: Abstract
OBJECTIVES
This study aimed to evaluate the association between long-term exposure to fine particulate matter (PM2.5) and cause-specific mortality among older adults in South Korea, providing insights into the evolving public health burden in an aging society.
METHODS
We analyzed national insurance claims data from the Republic of Korea spanning 2010–2019. Modeled PM2.5 concentrations were assigned to participants according to their residential districts. We employed time-varying Cox proportional hazard models, using age as the time scale, adjusted for potential confounders. Six cause-specific mortalities were considered: ischemic heart disease (IHD), stroke, chronic obstructive pulmonary disease (COPD), acute lower respiratory infection (ALRI), lung cancer (LC), and type 2 diabetes mellitus (T2DM). Annual excess deaths attributable to long-term PM2.5 exposure were calculated.
RESULTS
A total of 5,360,032 older adults were followed from 2010 to 2019. Hazard ratios (HRs) per 10 μg/m³ increase in 12-month PM2.5 concentration were as follows: IHD, 1.068 (95% CI, 1.040–1.097); stroke, 1.023 (95% CI, 1.003–1.043); ALRI, 1.050 (95% CI, 1.026–1.076); COPD, 1.114 (95% CI, 1.072–1.157); T2DM, 1.046 (95% CI, 1.007–1.086); and LC, 0.972 (95% CI, 0.948–0.996). Excess deaths attributable to long-term PM2.5 exposure were estimated at 4,888 (95% CI, 2,304–7,323) in 2010 and 5,179 (95% CI, 2,585–7,648) in 2019.
CONCLUSIONS
Although PM2.5 levels in South Korea have shown a declining trend over the past decade, mortality among older adults associated with long-term PM2.5 exposure has not significantly decreased, likely due to the rapid aging of the population.; Summary

Special article

The Korean National Codes Against Cancer: background of their establishment and the revision process: Yoonjoo Choi, Jin-Kyoung Oh, Ayoung Byeon, Byungmi Kim; Epidemiol Health. 2025;e2025027. Published online May 14, 2025; DOI: https://doi.org/10.4178/epih.e2025027 [Accepted]

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Abstract PDF: Abstract
OBJECTIVES
The Korean National Codes Against Cancer provide guidelines for cancer prevention. The inaugural edition was published in 2006, followed by a major revision in 2016. This study aimed to describe the historical context, scientific rationale, and revision process of these guidelines.
METHODS
With rising cancer incidence in the early 2000s, the Korean government recognized the need for national cancer prevention guidelines, prompting the National Cancer Center to initiate their formulation. The Division of Cancer Prevention reviewed global literature on cancer trends and Korea-specific studies on cancer risk factors. The final set of 10 recommendations comprising the Korean National Codes Against Cancer was approved by the National Cancer Control Committee after achieving expert consensus on cancer prevention.
RESULTS
The finalized guidelines are firmly grounded in scientific evidence. The 10 current recommendations include: (1) no smoking and avoidance of secondhand smoke; (2) consuming sufficient fruits and vegetables as part of a balanced diet; (3) reducing salt intake and avoiding burnt or charred foods; (4) limiting alcohol consumption; (5) engaging in regular physical activity (at least 30 minutes a day, 5 days a week); (6) maintaining a healthy body weight; (7) receiving immunization against hepatitis B virus and human papillomavirus; (8) practicing safe sex by maintaining a single sexual partner and using condoms; (9) following health and safety guidelines to avoid exposure to occupational carcinogens; and (10) undergoing regular cancer screening.
CONCLUSIONS
This study detailed the sources and procedures involved in formulating and revising the Korean National Codes Against Cancer.; Summary

Original articles

Adherence to the Korean National Code Against Cancer and mortality: a prospective cohort study from the Health Examinees-Gem study: Jeeyoo Lee, Aesun Shin, Woo-Kyoung Shin, Ji-Yeob Choi, Daehee Kang; Epidemiol Health. 2025;e2025026. Published online May 9, 2025; DOI: https://doi.org/10.4178/epih.e2025026 [Accepted]

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Abstract PDF: Abstract
OBJECTIVES
The Korean National Code Against Cancer was released in 2006. These guidelines aimed to promote a healthy lifestyle to prevent cancer risk through 10 recommendations. The objective of this study was to investigate the associations between adherence to the Korean National Code Against Cancer and the risk of all-cause, cancer, and cardiovascular disease (CVD) mortality among Koreans.
METHODS
This prospective cohort study included 109,160 Korean adults aged 40 to 69 years, recruited from 2004 to 2013 in the population-based Health Examinees-Gem Study (HEXA-G). The adherence total score was calculated based on 6 items from the Korean National Code Against Cancer: smoking, consuming vegetables and fruits, limiting salty foods, restricting alcohol intake, engaging in physical activity, and maintaining a healthy weight. Hazard ratios (HRs) and 95% confidence intervals (CIs) for the associations of adherence scores with mortality risk were estimated using a Cox proportional hazards regression model.
RESULTS
During a mean follow-up period of 12.0 years, 3,799 deaths were recorded. According to the multivariable-adjusted model, men in the highest tertile of adherence scores had a lower risk of all-cause, cancer, and CVD mortality compared to those in the lowest tertile (all-cause: HR=0.67, 95% CI=0.60–0.74; cancer: HR=0.63, 95% CI=0.54–0.74; CVD: HR=0.56, 95% CI=0.43–0.73). A similar association was observed among women for all-cause and CVD mortality (all-cause: HR=0.85, 95% CI=0.76–0.96; CVD: HR=0.70, 95% CI=0.51–0.97).
CONCLUSIONS
Adherence to the Korean National Code Against Cancer was associated with a reduced risk of all-cause, cancer, and CVD mortality.; Summary

Social capital and regional influences: key predictors of unmet dental care needs among older adults in South Korea: Ji-Yeon Lim, Ju-Mi Lee, Hae-Sung Nam; Epidemiol Health. 2025;e2025025. Published online May 7, 2025; DOI: https://doi.org/10.4178/epih.e2025025 [Accepted]

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Abstract PDF: Abstract
OBJECTIVES
Access to dental services is essential for improving quality of life, and social capital plays a key role in facilitating that access. This study aimed to identify individual- and regional-level factors, including social capital, that predict unmet dental care needs among older adults.
METHODS
We analyzed data from 59,414 older adults obtained from the 2023 Korea Community Health Survey and the Korean Statistical Information Service, employing a 2-level multilevel model. The dependent variables comprised 3 types of unmet dental care needs: overall, due to lack of acceptability, and due to economic reasons. Twelve independent variables, including social capital and other individual and regional factors, were examined.
RESULTS
The prevalence of unmet needs was 14.15% overall, 8.70% for acceptability reasons, and 4.85% for economic reasons. Lower individual social capital was associated with higher odds of unmet dental care needs, whereas regional social capital factors demonstrated no significant association. Residing in regions with higher fiscal independence ratios was related to an increased likelihood of economic unmet needs (odds ratio [OR], 1.29; 95% confidence interval [CI], 1.09 to 1.52). In contrast, a greater density of dentists per 10,000 population was inversely associated with overall and acceptability-related unmet needs (OR, 0.82 for both; 95% CI, 0.73 to 0.92 and 0.73 to 0.93, respectively).
CONCLUSIONS
Individual social capital and specific regional factors—namely, fiscal independence and density of dentists—may represent important determinants of unmet dental care needs among older adults. Policy interventions aimed at reducing unmet needs should consider these variables.; Summary

Risk of new-onset seizures following immunization against COVID-19: a self-controlled case-series study: Hwa Yeon Ko, Dongwon Yoon, Ju Hwan Kim, Han Eol Jeong, Seung Bong Hong, Won Chul Shin, JU YOUNG SHIN; Epidemiol Health. 2025;e2025024. Published online May 2, 2025; DOI: https://doi.org/10.4178/epih.e2025024 [Accepted]

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Abstract PDF: Abstract
OBJECTIVES
Despite emerging reports of new-onset seizures (NOS) following COVID-19 vaccination, safety evidence regarding the risk of NOS after vaccination remains limited. We aimed to investigate the potential association between NOS and COVID-19 vaccination.
METHODS
We conducted a self-controlled case series study utilizing a nationwide database linking the COVID-19 vaccination registry and the National Health Information Database (from February 2021 to October 2022). We identified adults (≥18 years) who received COVID-19 vaccination (BNT162b2, ChAdOx1 nCoV-19, mRNA-1273, NVX-CoV2373, or Ad26.COV2.S) and had a diagnosis of NOS accompanied by prescriptions of anti-seizure drugs. The observation period was defined as 240 days following vaccination. We evaluated the risk of NOS during a risk window of 28 days after vaccination compared to the control window (the remaining observation period excluding the risk window). Incidence rate ratios (IRRs) with 95% confidence intervals (CIs) were estimated using a conditional Poisson regression model.
RESULTS
Among 42,155,198 COVID-19 vaccine recipients, we identified 1,849 and 4,217 patients with NOS in the risk and control windows, respectively. There was no increased risk of NOS within the 28-day period following vaccination (IRR, 0.99; 95% CI, 0.94–1.05). Although results from subgroup analyses by vaccine type were largely consistent with the main findings (IRR, 0.95; 95% CI, 0.88–1.03 for BNT162b2; IRR, 0.95; 95% CI, 0.77–1.16 for ChAdOx1 nCoV-19; IRR, 1.58; 95% CI, 0.52–4.83 for Ad26.COV2.S), a marginally elevated risk was observed for mRNA-1273 (IRR, 1.21; 95% CI, 1.04–1.42).
CONCLUSIONS
There was no evidence of an increased risk of NOS following COVID-19 vaccination. These findings can be used as safety evidence in clinical decision-making and to bolster public confidence in COVID-19 vaccines.; Summary

Original Article

Association between humidifier disinfectant use duration and lung cancer development in Korea: Sungchan Kang, Jeong-In Hwang, Su Hwan Kim, Hyungryul Lim, Dong-wook Lee, Woojoo Lee, Jong Hun Kim, Sol Yu, Jungyun Lim, Younghee Kim, Kyoung-Nam Kim; Epidemiol Health. 2025;47:e2025023. Published online May 2, 2025; DOI: https://doi.org/10.4178/epih.e2025023

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Abstract Summary PDF: Abstract
OBJECTIVES
This study was conducted to assess the association between the duration of humidifier disinfectant use and lung cancer development.
METHODS
We analyzed data from 3,605 applicants registered for compensation from the Korean government due to health conditions related to humidifier disinfectant exposure. Among these individuals, 121 were diagnosed with lung cancer at least 4 years after their initial exposure (through December 2021). Hazard ratios (HRs) and 95% confidence intervals (CIs) for lung cancer incidence were estimated according to the duration of disinfectant use using Cox proportional hazards models.
RESULTS
Compared with <5 months of use, the HRs for lung cancer were 1.81 (95% CI, 0.41 to 7.97) for 5-14 months, 2.45 (95% CI, 0.58 to 10.41) for 15-29 months, and 4.61 (95% CI, 1.12 to 18.91) for ≥30 months. Using never smokers with <15 months of use as the reference category, the HRs were 2.97 (95% CI, 1.34 to 6.56) for never smokers with ≥15 months of use, 2.73 (95% CI, 0.94 to 7.95) for current or former smokers with <15 months of use, and 4.74 (95% CI, 1.94 to 11.61) for current or former smokers with ≥15 months of use.
CONCLUSIONS
Our study provides some of the first robust epidemiological evidence that prolonged humidifier disinfectant use contributes to lung cancer development. Future studies—particularly those including unexposed populations—are needed to confirm these findings.; Summary

Korean summary
* 장기간의 가습기 살균제 사용과 폐암 발생의 위험 간에는 정량적 연관성을 발견할 수 있었습니다. * 가습기살균제를 30개월 이상 사용했다고 응답한 사람들은, 가습기살균제를 5개월 미만 사용했다고 응답한 사람들과 비교하여 폐암 발생 위험이 4배 높았습니다.

Key Message
* There is a quantitative association between prolonged humidifier disinfectants use and the risk of lung cancer incidence. * Individuals reported they used humidifier disinfectants for more than 30 months had more than four times higher risk of lung cancer than those of individuals who reported they used humidifier disinfectants for less than five months.

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