Epidemiological Impact of the Korean National Immunization Program on Varicella Incidence

Pertussis epidemic in Korea and implications for epidemic control

The pertussis epidemic in Korea is ongoing, with a record-high incidence rate. Although pertussis incidence is high worldwide in 2024, the scale of the increase observed in Korea is unprecedented and incomparable to that in other countries. The high proportion of cases among children aged 5 to 14 years is the distinctive characteristics of the 2024 pertussis epidemic in Korea. To accurately interpret the epidemiological trend in pertussis incidence in Korea, validating the surveillance system and evaluating vaccine efficacy and effectiveness are essential.

A cost benefit analysis of varicella vaccination in South Korea

Background

The introduction of varicella vaccination has significantly reduced the burden of chickenpox in many countries, but outbreaks still occur in populations with high vaccination coverage. To address this, some countries, including the United States, Germany, and Japan, have adopted a two-dose varicella vaccination recommendation. Economic evaluations are crucial for assessing vaccine recommendations; however, there are limited studies exist in Asian countries. Thus, our study aimed to evaluate the cost-benefit of one-dose and two-dose varicella vaccination programs compared to no vaccination in South Korea, incorporating updated data on disease burden and costs.

Methods

We utilized data from South Korea's health databases to estimate varicella burden and vaccination records. Decision tree analysis was employed to compare costs and benefits of vaccination strategies over a ten-year period for the 2012 birth cohort. Sensitivity analyses were conducted to assess the impact of various variables.

Results

Both one-dose and two-dose vaccination programs showed cost-benefit compared to no vaccination, with substantial societal cost savings. The one-dose program yielded a benefit-cost ratio (BCR) of1.43, while the two-dose program had a direct BCR of1.28. Sensitivity analyses confirmed the robustness of these findings.

Conclusion

Our study demonstrates the economic benefits of varicella vaccination in South Korea, aligning with findings from other countries. While the second dose did not show additional cost savings compared to the one-dose program, other factors like disease severity and transmission dynamics should be considered. Implementing either a one-dose or two-dose varicella vaccination regimen in South Korea could lead to cost reductions and improved cost-effectiveness compared to no vaccination, emphasizing the importance of vaccination programs in reducing disease burden and enhancing public health outcomes.

Clinical and radiological features of a cluster of immunocompetent adolescents with varicella pneumonia: a descriptive study

Background

Varicella pneumonia is one of the most common and severe complications of chickenpox infection. This study aimed to describe the clinical and radiological features of varicella pneumonia in a cluster of immunocompetent adolescents.

Methods

A retrospective analysis was conducted on a cohort of adolescent patients diagnosed with varicella pneumonia at Wuhan Jinyintan Hospital between February 2023 and May 2023. The clinical and imaging data were collected and analyzed. A total of 116 patients were divided into two groups by the absence (group 1, n=57) or presence (group 2, n=59) of lower respiratory symptoms for data comparison.

Results

Among 116 patients (median age, 16 years; 60 males), rash (100%) was the most prevalent clinical symptom. The most common respiratory symptom and sign were fever (42.2%) and coarse breath sounds (41.4%). Chest computed tomography (CT) performed within five days of symptoms onset revealed multiple (89.7%), peripheral (51.7%), and ill-defined (73.3%) lung nodules in most patients, which gradually improved 6-10 days after symptom onset. Group 2 had higher levels of interleukin-6 (P<0.001), C-reactive protein (P=0.02), serum amyloid-A protein (P=0.002), longer hospital stays (P=0.04), more involved lung lobes (P=0.02), and a higher incidence of multiple nodules (P=0.043) than those of group 1.

Conclusions

In immunocompetent adolescents, clustered varicella pneumonia often presents as mild and more uniform in clinical and radiological presentations than sporadic cases. The most common CT findings were multiple pulmonary nodules. Patients with lower respiratory symptoms exhibited more severe clinical and radiological manifestations. Generally, it is not recommended that patients undergo frequent CT scans in a short period.

The impact of varicella vaccination: A 2005-2019 interrupted time series analysis

Varicella is an acute, highly contagious disease in susceptible individuals and is preventable through vaccination. This study aimed to determine the impact of varicella vaccination on hospitalizations and complications at a pediatric reference hospital in Panama before and after the vaccine introduction. This descriptive ecological study analyzed clinical records of patients diagnosed with varicella through a retrospective and interrupted time series analysis. An autoregressive integrated moving average model was built to compare the incidence rates observed after vaccination with those expected rates derived from the model. A statistical model was fitted to the observed interrupted time series data by regression and used to predict future trends. The mean difference in varicella hospital discharges before and after the introduction of the varicella vaccine was 47%. The rate of hospitalizations for varicella decreased to 52.3%. A declining trend in varicella hospitalizations was observed from 2015 after vaccine introduction in 2014. Complications in vaccinated patients were secondary skin and soft tissue infection, possibly due to bacterial superinfection. The impact of varicella vaccination on reducing varicella hospital discharges reported at a pediatric reference hospital in Panama was confirmed.

Estimation of single-dose varicella vaccine effectiveness in South Korea using mathematical modeling

In South Korea, despite the implementation of a universal single-dose vaccination program for children aged 12–15 months in 2005, the varicella incidence rate remains significant. Prior case-control studies have reported that currently used varicella vaccines are extremely inefficacious. We estimated vaccine effectiveness (VE) by fitting a dynamic transmission model to age-specific varicella incidence data from 2007 to 2015 and available vaccine coverage data. The initial vaccine efficacy and primary failure rates were estimated to be 61.1% and 38.9%, respectively. The average duration of protection was 21.4 years. The mean VE [(1-relative risk) %] for the simulated data of 2004–2014 birth cohorts decreased from 59.8% to 50.7% over 9 years. This mathematical modeling study demonstrated that the single-dose vaccine exhibits moderate effectiveness, and a high proportion of primary failure could be a main cause of breakthrough infections. Therefore, a two-dose vaccination strategy should be considered.

Epidemiological impact of universal varicella vaccination on consecutive emergency department visits for varicella and its economic impact among children in Kobe City, Japan

INTRODUCTION

Previous studies reported a dramatic decline in the incidence of varicella and varicella-related deaths after implementing universal varicella vaccination (VarV). Although previous studies reported the effectiveness and economic impact of VarV, they were unknown in the emergency department (ED) setting.

METHODS

To determine the effectiveness and economic impact of VarV in the ED, Kobe, Japan, we retrospectively reviewed the clinical database of consecutive patients younger than 16 years presenting to our primary ED from 2011 to 2019.

RESULTS

Of the 265,191 children presenting to our ED, 3,092 patients were clinically diagnosed with varicella. The number of patients with varicella was approximately 500 annually, before introducing the universal two-dose VarV for children aged 1 to <3 years in October 2014, in the Japanese national immunization program, and decreased to approximately 200 in 2019. The number of patients with varicella younger than 1 year (ineligible for the vaccination) also decreased. Regarding the economic impact, the medical cost in our ED reduced after the introduction of VarV was JPY 4.1 million (US$ 40,049) annually. From the central data, approximately 95% of children were vaccinated after October 2014; however, a relatively large percentage of infected unvaccinated children (59.0%) presented to ED in this study. After the implementation of the universal VarV, infection was mainly observed in older children (i.e., the unvaccinated generation).

CONCLUSIONS

Our data showed the effectiveness and economic impact of VarV in the ED setting. Additionally, our data suggested that the public vaccination program should include older unvaccinated children and other unvaccinated individuals.

Infectious Respiratory Diseases Decreased during the COVID-19 Pandemic in South Korea

Infectious respiratory diseases are highly contagious and very common, and thus can be considered as one of the leading causes of morbidity and mortality worldwide. We followed up the incidence rates (IRs) of eight infectious respiratory diseases, including chickenpox, measles, pertussis, mumps, invasive pneumococcal disease, scarlet fever, rubella, and meningococcal disease, after COVID-19 mitigation measures were implemented in South Korea, and then compared those with the IRs in the corresponding periods in the previous 3 years. Overall, the IRs of these diseases before and after age- or sex-standardization significantly decreased in the intervention period compared with the pre-intervention periods (p < 0.05 for all eight diseases). However, the difference in the IRs of all eight diseases between the IRs before and after age-standardization was significant (p < 0.05 for all periods), while it was not significant with regard to sex-standardization. The incidence rate ratios for eight diseases in the pre-intervention period compared with the intervention period ranged from 3.1 to 4.1. These results showed the positive effects of the mitigation measures on preventing the development of respiratory infectious diseases, regardless of age or sex, but we need to consider the age-structure of the population to calculate the effect size. In the future, some of these measures could be applied nationwide to prevent the occurrence or to reduce the transmission during outbreaks of these infections. This study provides evidence for strengthening the infectious disease management policies in South Korea.

Cross-Sectional Study of Varicella Zoster Virus Immunity in Healthy Korean Children Assessed by Glycoprotein Enzyme-Linked Immunosorbent Assay and Fluorescent Antibody to Membrane Antigen Test

The prevalence of varicella is especially high among children in the age group of 4-6 years in South Korea, regardless of vaccination. We investigated the immune status of healthy children enrolled in day-care centers and compared pre- and post-vaccination immunity. Antibody titers were measured using a glycoprotein enzyme-linked immunosorbent assay (gpEIA) kit, and the seroconversion rate was assessed using a fluorescent antibody to membrane antigen (FAMA) test. Among 541 vaccinated children, 109 (20.1%) had breakthrough varicella. However, 13 (72.2%) of the 18 unvaccinated children had a history of varicella. The gpEIA geometric mean titers (GMTs) of pre- and 5 weeks post-vaccination in 1-year-old children were 14.7 and 72 mIU/mL, respectively, and the FAMA seroconversion rate was 91.1%. The gpEIA GMTs of 2-, 3-, 4-, 5-, and 6-year-old children were 104.1, 133.8, 223.5, 364.1, and 353.0 mIU/mL, respectively. Even though the gpEIA GMT increased with age, the pattern of gpEIA titer distribution in 4- to 6-year-old vaccinees without varicella history represented both waning immunity and natural boosting immunity. These results suggest that some vaccinees are vulnerable to varicella infection. Therefore, it is necessary to consider a two-dose varicella vaccine regimen in South Korea.

Complementing conventional infectious disease surveillance with national health insurance claims data in the Republic of Korea

Surveillance remains an important tool for timely outbreak detection and response. Many countries, including Korea, have established national infectious disease surveillance systems with clinical notification. We aimed to evaluate the National Health Insurance Claims-based Surveillance (NHICS) compared to conventional passive report-based National Infectious Diseases Surveillance (NIDS). Reported to claimed cases ratios (R/C ratio) were evaluated from monthly notifiable disease cases captured by NIDS and NHICS. The relationships between 26 infectious diseases and each surveillance system were analysed using Pearson's correlation analysis and linear regression. There was an overall increase in R/C ratio from 2010-2017 (0.37 to 0.78). In 22 infectious diseases, there was a correlation between NIDS and NHICS. Moreover, claim-based surveillance showed less fluctuating disease incidence rates than report-based surveillance for specific infectious diseases, such as varicella, mumps, and scarlet fever. However, for infectious diseases with episodic outbreaks or low incidence, it was difficult to assess NHICS usefulness. Claim-based surveillance is less affected by limitations of conventional report-based surveillance systems, such as reporting rate. Given delays in claim systems, a claim-based surveillance is expected to be complementary to conventional systems for the detection of various infectious diseases with the advancement of bio-information technology.