A framework for nationwide COVID-19 vaccine safety research in the Republic of Korea: the COVID-19 Vaccine Safety Research Committee

With the introduction of coronavirus disease 2019 (COVID-19) vaccines, the Korea Disease Control and Prevention Agency (KDCA) commissioned the National Academy of Medicine of Korea to gather experts to independently assess post-vaccination adverse events. Accordingly, the COVID-19 Vaccine Safety Research Committee (CoVaSC) was launched in November 2021 to perform safety studies and establish evidence for policy guidance. The CoVaSC established 3 committees for epidemiology, clinical research, and communication. The CoVaSC mainly utilizes pseudonymized data linking KDCA’s COVID-19 vaccination data and the National Health Insurance Service’s claims data. The CoVaSC’s 5-step research process involves defining the target diseases and organizing ad-hoc committees, developing research protocols, performing analyses, assessing causal relationships, and announcing research findings and utilizing them to guide compensation policies. As of 2022, the CoVaSC completed this research process for 15 adverse events. The CoVaSC launched the COVID-19 Vaccine Safety Research Center in September 2022 and has been reorganized into 4 divisions to promote research including international collaborative studies, long-/short-term follow-up studies, and education programs. Through these enhancements, the CoVaSC will continue to swiftly provide scientific evidence for COVID-19 vaccine research and compensation and may serve as a model for preparing for future epidemics of new diseases.

Comparison of the Prevalence of Cardiometabolic Disorders and Comorbidities in Korea and the United States: Analysis of the National Health and Nutrition Examination Survey

Background@#Comparison of the prevalence of cardiometabolic disorders (CMDs) and comorbidities in Korea and the United States (US) can be an important indicator for forecasting future risk of cardiovascular events in Korea. This study aimed to estimate and compare the prevalence of hypertension, diabetes mellitus (DM), dyslipidemia, obesity, and metabolic syndrome (MetS) in Korea and the US. @*Methods@#A total of 15,872 individuals from the US National Health and Nutrition Examination Survey (NHANES) 2003–2014 and 26,492 from the Korea NHANES (KNHANES) 2007–2014 were included. Additionally, 164,339 (139,345 from the Health Examinees-Gem Study and 24,994 from the Cardiovascular Disease Association Study) participants enrolled in the Korea Genome and Epidemiology Study were included to investigate the differences of CMDs between urban and rural regions. To estimate the age-standardized prevalence of CMDs in individuals aged 40–69 years, direct standardization using the World Health Organization standard population was performed. @*Results@#The prevalence of CMDs was lower in Korea than the US (hypertension 49.9% vs.56.8%; DM 13.4% vs. 14.3%; hypercholesterolemia 16.8% vs. 17.8%; obesity 36.2% vs. 38.6%; and MetS 29.4% vs. 36.5%). According to the median survey years, dyslipidemia has become more prevalent in Korea than in the US since 2010. The prevalence of CMDs was greater in rural than that in urban areas in Korea. @*Conclusion@#The prevalence of dyslipidemia in Korea exceeded that of the US after 2010, which was associated with increasing burden of cardiovascular events. The present study suggests that further preventive strategies are needed to mitigate the prevalence of CMDs in Korea.

Adherence to the Recommended Intake of Calcium and Colorectal Cancer Risk in the HEXA Study / Journal of the Korean Cancer Association, 대한암학회지

Purpose@#Dietary calcium intake has been suggested to be protective against the development of colorectal cancer. The mean dietary calcium intake of Koreans is 490 mg/day, which is far below the recommended calcium intake of 700-800 mg/day. In this study, we explored the relationship between dietary calcium intake and colorectal cancer development in Koreans with relatively low calcium intake compared with individuals in Western countries. @*Materials and Methods@#The Health Examinees Study, a large-scale genomic community-based prospective cohort study, was designed to identify the general characteristics of major chronic diseases in Koreans. A total of 119,501 participants aged 40-69 years recruited between 2004 and 2013 were included in this analysis. The calcium intake level was categorized using the Dietary Reference Intakes for Koreans (KDRIs). The Cox proportional hazards regression model was used to estimate the hazard ratio (HR) and the corresponding 95% confidence intervals (CIs) for colorectal cancer risk, adjusting for potential confounders. @*Results@#In the multivariable-adjusted model, compared with the group that consumed less than the recommended amount of calcium, the group that consumed more than the recommended intake of calcium showed a significant reduction in the risk of colorectal cancer in women. (HR, 0.54; 95% CI, 0.31 to 0.95). Among men, however, no significant association was observed between dietary calcium intake and colorectal cancer risk (HR, 0.89; 95% CI, 0.54 to 1.45). @*Conclusion@#Korean women who adhere to the recommended intake of calcium showed a reduced risk of colorectal cancer.

How well does societal mobility restriction help control the COVID-19 pandemic? Evidence from real-time evaluation

ObjectivesTo determine the impact of restrictions on mobility on reducing transmission of COVID-19. DesignDaily incidence rates lagged by 14 days were regressed on mobility changes using LOESS regression and logit regression between the day of the 100th case in each country to August 31, 2020. Setting34 OECD countries plus Singapore and Taiwan. ParticipantsGoogle mobility data were obtained from people who turned on mobile device-based global positioning system (GPS) and agreed to share their anonymized position information with Google. InterventionsWe examined the association of COVID-19 incidence rates with mobility changes, defined as changes in categories of domestic location, against a pre-pandemic baseline, using country-specific daily incidence data on newly confirmed COVID-19 cases and mobility data. ResultsIn two thirds of examined countries, reductions of up to 40% in commuting mobility (to workplaces, transit stations, retailers, and recreation) were associated with decreased COVID-19 incidence, more so early in the pandemic. However, these decreases plateaued as mobility remained low or decreased further. We found smaller or negligible associations between mobility restriction and incidence rates in the late phase in most countries. ConclusionMild to moderate degrees of mobility restriction in most countries were associated with reduced incidence rates of COVID-19 that appear to attenuate over time, while some countries exhibited no effect of such restrictions. More detailed research is needed to precisely understand the benefits and limitations of mobility restrictions as part of the public health response to the COVID-19 pandemic. WHAT IS ALREADY KNOWN ON THIS TOPICSince SARS-CoV-2 became a pandemic, restrictions on mobility such as limitations on travel and closure of offices, restaurants, and shops have been imposed in an unprecedented way in both scale and scope to prevent the spread of COVID-19 in the absence of effective treatment options or a vaccine. Although mobility restriction has also brought about tremendous costs such as negative economic growth and other collateral impacts on health such as increased morbidity and mortality from lack of access to other essential health services, little evidence exists on the effectiveness of mobility restriction for the prevention of disease transmission. A search of PUBMED and Google Scholar for publications on this topic through Sep 20, 2020 revealed that most of the evidence on the effectiveness of physical distancing comes from mathematical modeling studies using a variety of assumptions. One study investigated only the combined effect of several interventions, including physical distancing, among SARS-CoV-2 infected patients. WHAT THIS STUDY ADDSThis is the first study to investigate the association between change in mobility and incidence of COVID-19 globally using real-time measures of mobility at the population level. For this, we used Google Global Mobility data and the daily incidence of COVID-19 for 36 countries from the day of 100th case detection through August 31, 2020. Our findings from LOESS regression show that in two-thirds of countries, reductions of up to 40% in commuting mobility were associated with decreased COVID-19 incidence, more so early in the pandemic. This decrease, however, plateaued as mobility decreased further. We found that associations between mobility restriction and incidence became smaller or negligible in the late phase of the pandemic in most countries. The reduced incidence rate of COVID-19 cases with a mild to moderate degree of mobility restriction in most countries suggests some value to limited mobility restriction in early phases of epidemic mitigation. The lack of impact in some others, however, suggests further research is needed to confirm these findings and determine the distinguishing factors for when mobility restrictions are helpful in decreasing viral transmission. Governments should carefully consider the level and period of mobility restriction necessary to achieve the desired benefits and minimize harm.

Association between Risk of Metabolic Syndrome and Stress in Each Occupational Group of KoreanWorkers: Korea National Health and Nutrition Examination Survey 2014–2016

Background@#Chronic stress at work is known to be associated with the risk of developing metabolic syndrome. Recent studies have evaluated stressand its association with metabolic syndrome in specific occupational groups. In the present study, we examined the relationship between stress andthe risk of developing metabolic syndrome in each occupational group. @*Methods@#The present study examined 7,460 Korean workers, aged 20–65 years, whose data were collected from the Korea National Health andNutrition Examination Survey conducted between 2014 and 2016. The information on usual stress awareness was self-reported, and thebiochemical profile of the blood was conducted. The chi-square test and multiple logistic regression analysis were used to investigate therelationship between stress and metabolic syndrome in each occupational group. @*Results@#The metabolic syndrome was prevalent in 26.3% of the study subjects. In the function-related job groups, the individuals with high stress levelsshowed a significantly higher risk of developing metabolic syndrome (odds ratio, 1.625; 95% confidence interval, 1.042–2.534) than those with lowstress levels. An increasing trend was observed, which suggested the increased risk of developing metabolic syndrome across increasing stress levelsin a stratified analysis in many occupational groups, specifically in function-related, viz., manager and expert, office worker, service worker, andsimple laborer (P for trend <0.001) groups. @*Conclusion@#The stress levels were significantly correlated with the risk of developing metabolic syndrome in function-related job groups. A differencebetween dose-response association of stress levels and metabolic syndrome existed in each occupational group.

Study Design for the 2016 Baseline Survey of a Health System Strengthening Project in Quoc Oai District, Hanoi, Vietnam

BACKGROUND: In order to provide essential scientific evidence on the population's health status and social health determinants as well as the current capacity of the health care system in Vietnam to health policy makers and managers, Vietnam Ministry of Health, Hanoi University of Public Health, Hanoi Medical University, and Ho Chi Minh University of Medicine and Pharmacy collaborated with Seoul National University (Korea) and conducted a health system survey in the Quoc Oai district (of Hanoi capital) that represented northern rural Vietnam. METHODS: The study design was a cross-sectional study. The survey covered different topics (more than 200 questions) and was administered in three separate questionnaires: 1) Basic information of all household members; 2) Household characteristics; and 3) Individual characteristics. Socio-demographic characteristics among the households and individuals were collected from 2,400 households sampled by multi-stage cluster sampling method: more than 200 questions. RESULTS: The household size of Quoc Oai was larger than the national average and there was no significant difference in gender composition. In addition, the proportions of pre-elderly, age 55–64, and elderly group (65 years old and over) were higher than the national population statistics. In this context, demographic transition has begun in Quoc Oai. CONCLUSION: This study design description provides the basic information about a baseline survey of a future prospective cohort (as a part of a collaborative project on strengthening the health system in Vietnam) to the prospective data user of this survey.

Effects of One-dose Varicella Vaccination on Disease Severity in Children during Outbreaks in Seoul, Korea

BACKGROUND: In Korea, the incidence of varicella has increased despite the introduction of a universal one-dose vaccination for children aged 12–15 months in 2005. A previous study demonstrated that the vaccine effectiveness was insufficient to prevent against varicella. We assessed the effect of the varicella vaccination on disease severity. METHODS: Epidemiologic investigation of varicella cases in Seoul metropolitan area from 2015 to 2017 were used. Varicella-related symptoms such as rash were determined by the clinical practitioners. Disease severity of patients was assessed by the number of skin lesions and divided into mild (≤ 50) and moderate (51–249) to severe (≥ 250). Unconditional logistic regression analysis was performed and age was controlled. RESULTS: Among a total of 1,008 varicella cases reported, 869 cases were breakthrough cases and 139 were unvaccinated cases. The risk for occurrence of moderate-to-severe disease in the breakthrough group was 0.57 times less than that of the unvaccinated group. CONCLUSION: These data suggest that national varicella vaccination may have a significant effect on attenuation of disease severity in children.

Association between Change in Alcohol Consumption and Metabolic Syndrome: Analysis from the Health Examinees Study

BACKGROUND: The association between change in alcohol intake and metabolic syndrome is unclear. METHODS: This retrospective cohort consisted of 41,368 males and females from the Health Examinees-GEM study. Participants were divided into non-drinkers (0.0 g/day), light drinkers (male: 0.1 to 19.9 g/day; female: 0.1 to 9.9 g/day), moderate drinkers (male: 20.0 to 39.9 g/day; female: 10.0 to 19.9 g/day), and heavy drinkers (male: ≥40.0 g/day; female: ≥20.0 g/day) for each of the initial and follow-up health examinations. Logistic regression analysis was used to determine the adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for developing metabolic syndrome according to the change in alcohol consumption between the initial and follow-up health examinations. Adjusted mean values for the change in waist circumference, fasting serum glucose (FSG), blood pressure, triglycerides, and high density lipoprotein cholesterol (HDL-C) levels were determined according to the change in alcohol consumption by linear regression analysis. RESULTS: Compared to persistent light drinkers, those who increased alcohol intake to heavy levels had elevated risk of metabolic syndrome (aOR, 1.45; 95% CI, 1.09 to 1.92). In contrast, heavy drinkers who became light drinkers had reduced risk of metabolic syndrome (aOR, 0.61; 95% CI, 0.44 to 0.84) compared to persistent heavy drinkers. Increased alcohol consumption was associated with elevated adjusted mean values for waist circumference, FSG, blood pressure, triglycerides, and HDL-C levels (all P<0.05). Reduction in alcohol intake was associated with decreased waist circumference, FSG, blood pressure, triglycerides, and HDL-C levels among initial heavy drinkers (all P<0.05). CONCLUSION: Heavy drinkers who reduce alcohol consumption could benefit from reduced risk of metabolic syndrome.

Primary Care Perspectives in Japan

With an increase in aging population and medical expenditure worldwide, primary care has been rising as a solution to these. Japan, a representative aging society which has the most elderly population in the world, also has tried to develop a primary care system and implemented many changes recently. Based on what authors experienced and observed at the points of care in Japan, we are going to review the primary care system and training strategy of family medicine in Japan and come up with some suggestions that could apply to Korea.

Validity of Self-reported Stroke and Myocardial Infarction in Korea: The Health Examinees (HEXA) Study / 예방의학회지

OBJECTIVES@#Self-reported disease history is often used in epidemiological studies. In this study, we acquired the hospital records of subjects who self-reported stroke or myocardial infarction (MI) and evaluated the validity of the participants’ self-reported disease history. We also determined the level of agreement between specialists and non-specialists.@*METHODS@#Among the participants in the Health Examinees study, 1488 subjects self-reported stroke or MI during 2012-2017, and medical records were acquired for the 429 subjects (28.8%) who agreed to share their medical information. Each record was independently assigned to 2 medical doctors for review. The records were classified as ‘definite,’‘possible,’ or ‘not’ stroke or MI. If the doctors did not agree, a third doctor made the final decision. The positive predictive value (PPV) of self-reporting was calculated with the doctors’ review as the gold standard. Kappa statistics were used to compare the results between general doctors and neurologists or cardiologists.@*RESULTS@#Medical records from 208 patients with self-reported stroke and 221 patients with self-reported MI were reviewed. The PPV of self-reported disease history was 51.4% for stroke and 32.6% for MI. If cases classified as ‘possible’ were counted as positive diagnoses, the PPV was 59.1% for stroke and 33.5% for MI. Kappa statistics showed moderate levels of agreement between specialists and non-specialists for both stroke and MI.@*CONCLUSIONS@#The validity of self-reported disease was lower than expected, especially in those who reported having been diagnosed with MI. Proper consideration is needed when using these self-reported data in further studies.

Seroprevalence of Middle East respiratory syndrome coronavirus (MERS-CoV) in public health workers responding to a MERS outbreak in Seoul, Republic of Korea, in 2015

@#The first case of Middle East respiratory syndrome coronavirus (MERS-CoV) in the Republic of Korea was confirmed in May 2015 after a traveller returned from the Middle East. There were 186 cases, including 38 deaths, within two months. The potential of a single MERS-confirmed patient to result in such a large MERS outbreak constitutes a serious global health concern.

An association between diet quality index for Koreans (DQI-K) and total mortality in Health Examinees Gem (HEXA-G) study

BACKGROUND/OBJECTIVES: Diet quality scores or indices, based on dietary guidelines, are used to summarize dietary intake into a single numeric variable. The aim of this study was to examine the association between the modified diet quality index for Koreans (DQI-K) and mortality among Health Examinees-Gem (HEXA-G) study participants. SUBJECTS/METHODS: The DQI-K was modified from the original diet quality index. A total of 134,547 participants (45,207 men and 89,340 women) from the HEXA-G study (2004 and 2013) were included. The DQI-K is based on eight components: 1) daily protein intake, 2) percent of energy from fat, 3) percent of energy from saturated fat, 4) daily cholesterol intake, 5) daily whole-grain intake, 6) daily fruit intake, 7) daily vegetable intake, and 8) daily sodium intake. The association between all-cause mortality and the DQI-K was examined using Cox proportional hazard regression models. Hazard ratios and confidence intervals were estimated after adjusting for age, gender, income, smoking status, alcohol drinking, body mass index, and total energy intake. RESULTS: The total DQI-K score was calculated by summing the scores of the eight components (range 0–9). In the multivariable adjusted models, with good diet quality (score 0–4) as a reference, poor diet quality (score 5–9) was associated with an increased risk of all-cause mortality (hazard ratios = 1.23, 95% confidence intervals = 1.06–1.43). Moreover, a one-unit increase in DQI-K score resulted in a 6% higher mortality risk. CONCLUSIONS: A poor diet quality DQI-K score was associated with an increased risk of mortality. The DQI-K in the present study may be used to assess the diet quality of Korean adults.

Implementing Expanded Rapid Human Immunodeficiency Virus Testing in Public Health Centers in Seoul, 2015 / 감염과화학요법

In 2015, rapid human immunodeficiency virus (HIV) testing was implemented in all 25 public health centers in Seoul. During March and December 2015, 20,987 rapid HIV tests were performed, of which 116 (0.5%) were positive. Compared to those of the period before application of the rapid HIV test in place of conventional enzyme immunoassay method, the number of HIV tests performed and the number of positive results increased by sevenfold and twofold, respectively. In conclusion, expansion of the provision of rapid HIV tests in public health centers increased the number of voluntary HIV tests.

The development of a community-based medical education program in Korea / 한국의학교육

PURPOSE: The introduction of community-based medical education would help improve the quality of primary care. This paper suggests learning objectives and an educational program for community-based medical education. METHODS: The educational program was developed in a 1-day consensus workshop. Twenty experts, including faculty members from family medicine department of a college of medicine in Seoul and community-based preceptors, participated in the program. A needs-assessment survey was conducted among community-based preceptors before the workshop. Through this workshop, we derived learning objectives and a standardized curriculum for community-based medical education. RESULTS: In the questionnaire before the workshop, community-based preceptors voiced concerns over the program's potential costs and the time required for teaching. The learning objectives and educational programs derived from the workshop's consensus were consistent with the characteristics of the primary care. Based on the results of this workshop, the joint expert team developed a standard educational program on two core topics: clinical teaching and mentoring. CONCLUSION: From this curriculum development process, participants could construct a more standardized curriculum for community-based medical education. Future studies are needed to evaluate the long-term outcomes of these educational programs, such as the learners' satisfaction and achievement.

Cost-Effectiveness of Voluntary HIV Testing Strategies in a Very Low-Prevalence Country, the Republic of Korea

BACKGROUND: The Republic of Korea has a very low prevalence of human immunodeficiency virus (HIV) infection, but the number of new HIV diagnoses has steadily risen, strongly indicating a large number of undetected HIV infections. Thus, it is important for Korean public health authorities to adopt and encourage cost-effective HIV detection tools, such as rapid HIV screening tests. In this study, we aimed to evaluate the cost-effectiveness of enzyme-linked immunosorbent assays (ELISA) and rapid tests in a public health center (PHC) setting. METHODS: We developed a decision analytic model to assess the per-examinee cost and the cost-effectiveness of identifying HIV patients in a PHC setting using two HIV testing strategies: conventional HIV screening by ELISA versus rapid HIV testing. Analysis was performed in two scenarios: HIV testing in an average-risk population and in a high-risk population. RESULTS: Compared to the ELISA, the rapid test was cost-saving and cost-effective. The per-examinee cost was USD 1.61 with rapid testing versus USD 3.38 with ELISA in an average-risk population, and USD 4.77 with rapid testing versus USD 7.62 with ELISA in a high-risk population. The cost of identifying a previously undiagnosed HIV case was USD 26,974 with rapid testing versus USD 42,237 with ELISA in an average-risk population, and USD 153 with rapid testing versus USD 183 with ELISA in a high-risk population. CONCLUSION: Rapid testing would be more cost-effective than using conventional ELISA testing for identifying previously undiagnosed HIV-infected cases in Korea, a country with extremely low HIV prevalence.

Implementing Expanded Rapid Human Immunodeficiency Virus Testing in Public Health Centers in Seoul, 2015 / 감염과화학요법

In 2015, rapid human immunodeficiency virus (HIV) testing was implemented in all 25 public health centers in Seoul. During March and December 2015, 20,987 rapid HIV tests were performed, of which 116 (0.5%) were positive. Compared to those of the period before application of the rapid HIV test in place of conventional enzyme immunoassay method, the number of HIV tests performed and the number of positive results increased by sevenfold and twofold, respectively. In conclusion, expansion of the provision of rapid HIV tests in public health centers increased the number of voluntary HIV tests.

Clinical and Epidemiologic Characteristics of Spreaders of Middle East Respiratory Syndrome Coronavirus during the 2015 Outbreak in Korea

Nosocomial transmission is an important characteristic of Middle East Respiratory Syndrome Coronavirus (MERS-CoV) infection. Risk factors for transmission of MERS-CoV in healthcare settings are not well defined. During the Korean outbreak in 2015, 186 patients had laboratory-confirmed MERS-CoV infection. Those suspected as a source of viral transmission were categorized into the spreader groups (super-spreader [n = 5] and usual-spreader [n = 10]) and compared to the non-spreader group (n = 171). Body temperature of ≥ 38.5°C (adjusted odds ratio [aOR], 5.54; 95% confidence interval [CI], 1.38–22.30; P = 0.016), pulmonary infiltration of ≥ 3 lung zones (aOR, 7.33; 95% CI, 1.93–27.79; P = 0.003), and a more nonisolated in-hospital days (aOR, 1.32 per 1 day; 95% CI, 1.09–1.60; P = 0.004) were significant risk factors in the spreader group. There was no different clinical factor between super-spreaders and usual-spreaders. Nonisolated in-hospital days was the only factor which tended to be higher in super-spreaders than usual-spreaders (Mean, 6.6 vs. 2.9 days; P = 0.061). Early active quarantine might help reducing the size of an outbreak.

An Outbreak of Measles in a University in Korea, 2014

Measles has been declared eliminated from the Korea since 2006. In April 2014, a measles outbreak occurred at a University in Seoul. A total of 85 measles cases were identified. In order to estimate vaccine effectiveness of measles vaccine, we reviewed the vaccination records of the university students. The vaccine effectiveness of two doses of measles containing vaccine was 60.0% (95% CI, 38.2–74.1; P < 0.05). Transmission was interrupted after the introduction of outbreak-response immunization. The outbreak shows that pockets of under-immunity among college students may have facilitated the disease transmission despite the high 2-dose vaccination coverage in the community.

Evaluation of an extracurricular program for students interested in rural and public health / 한국의학교육

PURPOSE: The problem regarding the geographic imbalance of the physician workforce has been a long-standing problem in South Korea. Additionally, rural medicine and public health have been marginalized across whole undergraduate curriculums. The aim of this study was to evaluate the effectiveness of an extracurricular program targeting medical students interested in rural and public health. METHODS: A 2-day extracurricular program was held twice in 2015 and 2016. A total of 53 students were selected among eighty students who voluntarily applied to participate in the program. The effectiveness of the program was evaluated by pre- and post-program surveys. RESULTS: The overall satisfaction for the program was 5.35 out of 6. The participants showed a significant improvement in perception of the clerkship experience in a rural and public health care setting as well as the importance of rural medicine and public health in South Korea. CONCLUSION: In conclusion, this study showed the acceptability of a short-term extracurricular program for medical students interested in rural and public health.

Effectiveness of Varicella Vaccination Program in Preventing Laboratory-Confirmed Cases in Children in Seoul, Korea

A universal one-dose varicella vaccination program was introduced in 2005 in Republic of Korea. However, the incidence of varicella in Korea has tripled over the last decade. We conducted a community based 1:1 matched case-control study to assess the effectiveness of one MAV strain-based vaccine and three Oka strain-based vaccines licensed for use in Korea. All cases were children in Seoul, Korea with varicella who were reported to the National Notifiable Disease Surveillance System in Seoul during 2013. The controls were age-matched children with mumps or scarlet fever but no history of varicella. We included 537 cases and 537 controls. The overall effectiveness of one dose of varicella vaccination was 13% (95% confidence interval [CI], −17.3–35.6). Of the four licensed varicella vaccines, only one was highly effective (88.9%; 95% CI, 52.1–97.4). The vaccine effectiveness for the other vaccines were 71.4% (95% CI, −37.5–94.1), −5% (95% CI, −61.9–31.9), and −100% (95% CI, −700–50.0). The overall effectiveness of vaccination was 75.8% (95% CI, 22.8–92.4) in the first year after vaccination and decreased thereafter; the effectiveness became −7.2% (95% CI, −130.9–59.2) in the fourth year after vaccination. Further studies are warranted to investigate reduced effectiveness of varicella vaccines in Korea.