Epidemiology and Health

Original Articles

Epidemiological features of the 2024 pertussis outbreak in Gyeonggi Province, Korea: Yeon Hwa Chang, Kyujin Chang, Yeong Jun Ju; Epidemiol Health. 2025;47:e2025072. Published online December 13, 2025; DOI: https://doi.org/10.4178/epih.e2025072

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Abstract Summary PDF: Abstract
OBJECTIVES
In 2024, Korea experienced a nationwide pertussis epidemic, with Gyeonggi Province accounting for nearly one-third of reported cases. This study investigated the epidemiological characteristics of the outbreak and explored the association between vaccination history and healthcare utilization.
METHODS
We analyzed 14,275 pertussis cases reported in Gyeonggi Province in 2024 using de-identified national surveillance data. Comparisons were performed by age group (<20 vs. ≥20 years) and vaccination status (<20 years). The chi-square and Mann–Whitney <i>U</i> tests were used, and effect sizes were assessed using Cramér’s V.
RESULTS
Of all cases, 89.8% occurred in individuals <20 years, particularly those aged 10-14 years. Children and adolescents were more often involved in clusters and had more identified contacts than adults, whereas adults had higher rates of hospitalization (13.2 vs. 5.9%) and emergency visits (4.4 vs. 0.9%; p<0.001). Among individuals <20 years, hospitalization was more common in the unvaccinated or unknown group (11.7%) than in the fully (5.9%) or partially vaccinated (5.5%) groups (p=0.045).
CONCLUSIONS
The epidemic was concentrated in school-aged populations, particularly adolescents. While vaccination status showed a limited association with healthcare utilization, individuals who were unvaccinated or had an undocumented vaccination history experienced delayed diagnosis and higher care needs. These findings highlight the importance of strengthening adolescent-focused vaccination strategies and preparedness for future pertussis outbreaks.; Summary

Korean summary
2024년 한국의 백일해 유행에 대해 총 인구의 1/4이 거주하는 경기도 유행을 분석한 결과, 학령기 청소년에 집중적으로 발생하였으며 미접종 또는 접종력 불명확일 때 진단 지연 및 더 많은 의료 이용과 연관되었다. 백일해 재유행 예방을 위해서는 청소년에 초점을 맞춘 전략 개선이 필요하다.

Key Message
Analysis of the pertussis epidemic in Gyeonggi Province, home to one quarter of the national population, during the 2024 outbreak in Korea showed that cases were concentrated among school-aged adolescents. Individuals who were unvaccinated or had an undocumented vaccination history experienced delayed diagnosis and higher care needs. Improving adolescent-focused prevention strategies is essential to prevent pertussis re-emergence.

Recent increase in pertussis incidence in Korea: an age-period-cohort analysis: Chanhee Kim, Seonju Yi, Sung-il Cho; Epidemiol Health. 2021;43:e2021053. Published online August 18, 2021; DOI: https://doi.org/10.4178/epih.e2021053

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10 Web of Science
12 Crossref

Abstract Summary PDF Supplementary Material

Abstract

OBJECTIVES
Pertussis or whooping cough—one of the most contagious diseases—is caused by the Gram-negative bacterium <i>Bordetella pertussis</i>. Despite a high vaccination rate, Korea recently experienced a resurgence of pertussis. This study explores patterns and possible explanations for this resurgence through an age-period-cohort analysis.

METHODS

Using secondary data from the infectious disease portal of the Korea Disease Control and Prevention Agency and the Korea Statistical Information Service of Statistics Korea, this study analyzed the incidence of pertussis in Korea to determine which factors contributed to the recent increase using an age-period-cohort model.

RESULTS

Analysis of the age effect indicated that the age group most vulnerable to pertussis was 0-year to 2-year-olds. Analysis of the period effect showed a sharp increase in the incidence rate after 2016. Analysis of the cohort effect showed a significant decrease in incidence beginning with the 1955 birth cohort, with the risk increasing again with the 2000s birth cohort.

CONCLUSIONS

Previous studies have suggested 3 main possible explanations for our results. First, the increased incidence rate can be attributed to contact rates. Second, the rate of immunity through natural exposure has decreased due to the low number of circulating pathogens, in turn affecting the trend of infection. Lastly, variations in pathogens may have also contributed to the increase in incidence. Given that the most significant increase in incidence was observed among infants younger than 1 year old, sufficient maternal immunity must be prioritized to provide passive immunity to newborns via the placenta.

Summary

Korean summary
본 연구는 연령-기간-코호트 모델을 활용하여 예방접종률이 높은 국가들의 백일해 재출현에 기여하는 요인에 무엇이 있는지 살펴보았다. 연령에 따른 사회적 접촉률(contact rate)의 변화, 자연노출에 의한 면역 강화(natural boosting) 기회의 감소, 그리고 백일해 병원체의 변이가 백일해 재출현의 원인일 수 있다. 분석 결과 영아 집단에서 백일해 발병률이 가장 급격한 증가가 관찰되었으며, 이는 모성면역의 확보가 중요하다는 점을 시사한다.

Key Message
This study examined factors contribute to the re-emergence of pertussis in countries with high vaccination rates using the age-period-cohort model. Changes in social contact rates according to age, reduction in immune boosting opportunities by natural exposure, and variations in pertussis pathogens may be the cause of re-emergence. As a result of the analysis, the sharpest increase in the incidence of pertussis in the infant group was observed, suggesting that securing maternal immunity is important.

Citations

Citations to this article as recorded by

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Epidemiological features of the 2024 pertussis outbreak in Gyeonggi Province, Korea
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