Waning Effectiveness of One-dose Universal Varicella Vaccination in Korea, 2011-2018: a Propensity Score Matched National Population Cohort

Assessing the effectiveness of the varicella vaccine in primary and secondary school students in Qingdao, China: A matched case-control study

OBJECTIVES

The effectiveness of varicella vaccination strategies needs to be further evaluated. The vaccine effectiveness (VE) of the varicella vaccine was evaluated, and changes in VE of varicella vaccination in primary and secondary school students in Qingdao, China, over time were analyzed.

PATIENTS AND METHODS

We conducted a 1:3 matched case-control study, using data from the Chinese Information System for Disease Control and Prevention, Qingdao Student Health Examination Management System, and Qingdao Immunization Program Information System. VE of the varicella vaccination was estimated using conditional logistic regression modeling.

RESULTS

A total of 3,249 varicella cases and 9,747 matched controls were included. One- and two-dose varicella vaccination had VE of 31.95 % (95 % confidence interval [CI]: 25.05 %-38.20 %) and 82.02 % (95 % CI: 78.33 %-85.07 %), respectively, and the incremental VE (two-dose versus one-dose vaccination) was 73.57 % (95 % CI: 68.26 %-78.00 %). VE remained at 71.46 % 10 years after the two-dose varicella vaccination, compared with a considerable decrease in VE to 29.73 % approximately 3-5 years after the one-dose varicella vaccination. VE of two-dose varicella vaccination was not related to the time interval between the two doses. The risk of varicella infection decreases with the number of doses of varicella vaccine received and with the age at which the first dose is given and increases with time after the last dose.

CONCLUSIONS

Two-dose varicella vaccination provides better protection for children and is therefore recommended for inclusion in China's national immunization program.

Social vs. individual age-dependent costs of imperfect vaccination

In diseases with long-term immunity, vaccination is known to increase the average age at infection as a result of the decrease in the pathogen circulation. This implies that a vaccination campaign can have negative effects when a disease is more costly (financial or health-related costs) for higher ages. This work considers an age-structured population transmission model with imperfect vaccination. We aim to compare the social and individual costs of vaccination, assuming that disease costs are age-dependent, while the disease's dynamic is age-independent. A model for pathogen deterministic dynamics in a population consisting of juveniles and adults, assumed to be rational agents, is introduced. The parameter region for which vaccination has a positive social impact is fully characterized and the Nash equilibrium of the vaccination game is obtained. Finally, collective strategies designed to promote voluntary vaccination, without compromising social welfare, are discussed.

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.

Seroprevalence of varicella-zoster virus as measured by fluorescent antibody to membrane antigen assay and glycoprotein enzyme-linked immunosorbent assay more than 10 years after initiation of a universal vaccination program: An observational study

Universal varicella vaccination (UVV), as a single dose to children aged 12 to 15 months, was introduced in Korea in 2005. A seroprevalence study is required to upgrade this UVV strategy. The fluorescent antibody to membrane antigen (FAMA) assay is the gold standard for varicella-zoster virus (VZV) immunity testing. However, no standard operating procedure (SOP) has been developed for the FAMA assay, in which either glutaraldehyde or acetone may be used for VZV-infected cell fixation. In this observational study, we aimed to investigate the age-specific seroprevalence in Korean children and adults. Additionally, with glycoprotein enzyme-linked immunosorbent assay (gpELISA) as the reference, we evaluated the performance of the FAMA assay using acetone-fixed cells. Four hundred sera were analyzed using the FAMA assay (acetone-fixed cells) and gpELISA, comprising 50 subjects from each age category. In the FAMA assay, the seropositivity rate decreased from 82.0% in the 1 to 4-year-old group to 58.0% in the 5 to 9-year-old group (95% confidence interval [CI]: 69.2-90.2 and 44.2-70.6, respectively; P = .009), while that in the gpELISA decreased from 80.0% to 52.0% (95% CI: 67.0-88.8 and 38.5-65.2, respectively; P = .003). In both methods, the seropositivity rates ranged from 95% to 100% in the population aged ≥ 20 years. We observed a significant correlation between the 2 methods, with a correlation coefficient of 0.795 (P < .001). In receiver operating characteristic analysis using the gpELISA results as a reference, the area under the curve for the FAMA assay was very high at 0.995 (95% CI: 0.990-1.000; P < .001). Compared to the gpELISA, the sensitivity, specificity, and kappa value of the FAMA assay were 99.4%, 79.3%, and 0.84 (nearly perfect), respectively. The seropositivity rate of the 5 to 9-year-old group indicated waning immunity over time and supported implementation of a second dose in the UVV program. The results of the FAMA assay were comparable to those of the gpELISA. Although further study is needed to standardize procedures, our results suggest that the FAMA assay using acetone-fixed cells can be used widely and can be included in a universal FAMA assay SOP.

Safety of Interchanging the Live Attenuated MAV/06 Strain and OKA Strain Varicella Vaccines in Children

Two live attenuated varicella vaccine (VZV) strains have been mainly used across the globe: MAV/06 and OKA strains. We aimed to explore the safety of interchanging the two VZV strains for primary and booster immunizations. South Korea's vaccine adverse event reporting system (VAERS) was accessed and searched to find filed reports of all adverse events (AEs) following immunization with the second dose of the varicella vaccine. The electronic medical records were reviewed for all visits to the hospital following the second dose of the varicella vaccine. Of the total 406 study participants, 27.5% (n = 112) were in the MAV/06-MAV/06 group, 30.3% (n = 123) in the MAV/06-OKA, 17.5% (n = 71) in the OKA-MAV/06 group, and 24.6% (n = 100) in the OKA-OKA group. Mean age at immunization with the first dose was 1.10 (standard deviation [SD] ±0.34) years old, and second dose was 4.77 (SD ± 1.13) (p = 0.772 and 0.933, respectively). There were no filed reports of AEs following the second dose in the national VAERS. Hospital visit records showed a total of 10.3% (95% confidence interval [CI], 7.6-13.7) (n = 42) had recorded AEs following the 2nd administered dose; however, only 0.7% (95% CI, 0.2-2.4) (n = 3) were regarded as possibly vaccine related. Two patients in the MAV/06-OKA group were diagnosed with Henoch-Schonlein purpura after the second dose; however, both had also received the MMR vaccine on the same day. No safety signals associated with interchanging the MAV/06 and OKA strain live attenuated varicella vaccines were observed in this patient cohort of healthy children.

Global varicella vaccination programs

Varicella (chickenpox) is an infectious disease caused by the highly contagious varicella zoster virus with a secondary attack rate greater than 90%. From this perspective, we aimed to establish the basis for a national varicella vaccine policy by reviewing vaccination programs and policies of countries that have introduced universal varicella vaccinations. As a result of the spread of varicella, an increasing number of countries are providing 2-dose vaccinations and universally expanding their use. In practice, the efficacy and effectiveness of vaccination differ among vaccines and vaccination programs. Optimized vaccination strategies based on each country's local epidemiology and health resources are required. Accordingly, it is necessary to evaluate the effectiveness of varicella vaccines in different settings. Given the short-term and fragmented vaccine effectiveness evaluation in Korea, it is necessary to evaluate its effectiveness at the national level and determine its schedule based on the evidence generated through these studies.

Evaluating the impact of universal varicella vaccination among preschool-aged children in Qingdao, China: An interrupted time-series analysis

Varicella is a contagious disease of children. Qingdao administrated free one-dose and free two-dose universal varicella vaccination schedules in 2013 and 2016 for preschool children. The effectiveness of the vaccination was analyzed in this study. Monthly varicella incidence data of 1-6 years old children during 2007-2020 were obtained from the Qingdao Infectious Disease Reporting Information Management System. We applied Interrupted time series and segmented regression analyses to assess changes in varicella incidence at the beginning of each month and average monthly changes during the vaccination. The vaccination was associated with a reduction of 32.7% in varicella morbidity on average during the 8-year intervention, there is a statistically significant difference between the voluntary period and free vaccination period (χ² = 290.80,P < 0.001). Immediately after the free one-dose vaccination implementation in 2013 and free two-dose vaccination implementation in 2016, varicella incidence decreased by 0.135 cases per 100 000 population (P < 0.001) and increased by 1.189 cases per 100 000 population (P = 0.039), respectively, the results were statistically significant. There were significant declining trends in varicella incidence after free vaccination: 0.135(P < 0.001) and 0.055 (P = 0.025) per month in 2013.7-2016.6 and 2016.7-2020.12, respectively. This study shows a further decaying trend of varicella incidence based on the impact of free two-dose vaccination. It is necessary to prolong free two-dose universal varicella vaccination to strengthen the immune barrier of preschool children sequentially.

Long-term vaccine efficacy of a 2-dose varicella vaccine in China from 2011 to 2021: A retrospective observational study

Objective

A 2-dose varicella vaccine immunization strategy has been implemented in many cities in China, but there is few evidence on a long-term evaluation of the efficacy of the 2-dose varicella vaccine from China. This study aims to assess the long-term vaccine efficacy of the two doses varicella vaccine and analysis of its influencing factors.

Methods

A retrospective study was carried out in 837,144 children born between 2011 and 2017 in Ningbo, Easten China. The logistic regression was performed to estimate varicella vaccine effectiveness (VE).

Results

The overall VE of 2 doses of varicella vaccine compared without the vaccine was 90.31% (89.24-91.26%), and the overall incremental VE of 2 doses of varicella vaccine compared to the 1-dose was 64.71% (59.92-68.93%). Moreover, the varicella vaccination age of the second dose and the interval between 2 doses were both associated with VE. The VE compared to that without the vaccine in children vaccinated at <4 years old was 91.22% (95%CI: 90.16-92.17%) which was higher than in children vaccinated at ≥4 years old (VE: 86.79%; 95%CI: 84.52-88.73). And the effectiveness of the vaccine was 93.60% (95%CI: 92.19-94.75%) in children with the interval of the 2 doses ≤ 24 months significantly higher than in children with the interval of ≥36 months (VE: 85.62%, 95%CI: 82.89-87.91%).

Conclusions

This study provides evidence for long-term VE of the 2-dose varicella vaccine and the better age for 2-dose vaccination and the interval between 2 doses of the vaccine in China.

Epidemiological characteristics of varicella outbreaks in the Republic of Korea, 2016–2020

Objectives

We described the trends and epidemiological characteristics of varicella outbreaks from 2016 to 2020 in the Republic of Korea.

Methods

We investigated variables such as the outbreak setting, age of patients, vaccination status, and lesion count. The collected data were analyzed with the Cochrane-Armitage trend test and Kruskal-Wallis test. These statistical tests were performed using R ver. 4.0.3.

Results

The number of varicella outbreaks increased from 2016 to 2018; however, after a slight decrease in the number of outbreaks in 2019, the number fell sharply in 2020. The median size of outbreaks decreased from 8 to 9 cases during 2016−2019 to 6 cases in 2020. The median duration of outbreaks was 18 days during 2016−2017, 28 days in 2018, 29 days in 2019, and 15 days in 2020. Varicella outbreaks occurred most frequently in elementary schools, and vaccination coverage of patients increased from 89.4% in 2016 to 97.2% in 2019. The median age of patients with outbreak-related varicella decreased from 8 years in 2016 to 6 years in 2020.

Conclusion

Significant changes were observed in the age of patients with outbreak-related varicella. Ongoing monitoring of varicella outbreaks should be conducted. Further research will be needed to measure the disease burden of varicella and enable evidence-based policy decisions.

Clinical Manifestations of Herpes Zoster Associated with Complications in Children

Herpes zoster (HZ) is caused by latent varicella-zoster virus (VZV) reactivation when VZV-specific cell-mediated immunity declines. Information on HZ in children is limited. Therefore, we retrospectively investigated HZ's clinical course and complications in children. We extracted the outpatient and hospitalization medical records of pediatric patients (<19 years) primarily diagnosed with HZ (ICD-10 B02 code) between January 2010 and November 2020. HZ was defined as a typical unilateral dermatomal vesicular rash where HZ was the treating physician's primary diagnosis. Recognized HZ complications included combined bacterial skin infection, ophthalmic zoster, zoster oticus without facial paralysis, meningitis, and PHN. We identified 602 HZ cases, among which 54 developed HZ complications and were included in our analysis. The median age was 14.7 years, most patients were aged ≥13 years (42, 79%), and none were aged <4 years. Fifty-three were immunocompetent, and only one had systemic lupus erythematosus. The most frequent complication was zoster ophthalmicus (n = 26, 48%). HZ complications were also observed in immunocompetent or vaccinated children exhibiting a head or neck rash before and after VZV immunization. Current VZV vaccination programs may be insufficient in preventing HZ complications. Therefore, close varicella and HZ burden monitoring and the establishment of effective VZV vaccination programs are imperative.