Trends in varicella and herpes zoster epidemiology before and after the implementation of universal one-dose varicella vaccination over one decade in South Korea, 2003–2015

Abstract

Background: In South Korea, the one-dose varicella vaccine was included in the National Immunization Program for children aged 12-15 months in 2005, and the vaccine coverage reached >95%. The impact of varicella vaccination on varicella and herpes zoster (HZ) was investigated, accounting for demographic changes over time. Methods: We calculated the crude and age-sex standardized incidence rates (IRs) and age-specific IRs of varicella and HZ from 2003 to 2015, using the National Health Information Database including approximately 50 million Koreans. The annual incidence rate ratios (IRRs) were calculated using a negative binomial regression analysis, adjusting for age and sex. Results: The crude varicella IR steadily declined by 67%, from 5.70/1000 to 1.87/1000 person years (IRR per year: 0.91; 95% CI 0.89-0.93), but the adjusted IRs showed a significant decline only during 2010-2015 (adjusted IRR per year: 0.90; 95% CI 0.88-0.93). The greatest decline was found in children ≤4 years of age, whereas the IR increased until 2011 and then declined afterward in children aged 5-9 years, who represented the highest incidence age group in 2013-2015. The crude HZ IR increased from 2.67/1000 to 9.80/1000 person years (IRR per year: 1.12; 95% CI 1.10-1.15), and the adjusted IR also followed the same trend. A similar increasing trend was observed before and after universal vaccination. Conclusions: One-dose varicella vaccination was moderately effective in preventing varicella, but this strategy was insufficient to interrupt varicella transmission in children. Furthermore, the HZ incidence dramatically increased over this decade. The current vaccination strategy against varicella-zoster disease should be reconsidered.

Epidemiological Impact of Universal Varicella Vaccination on Consecutive Emergency Department Visits for Varicella and Its Cost-Effectiveness Among Children

“…The present study clearly showed that the age of varicella patients who presented to our ED has increased since the implementation of the universal two-dose VarV. Previous studies also reported that the occurrence of varicella has shifted to older children [9,20]. Qin et al reported the shift of varicella to older children after the implementation of one-dose VarV in Lu'an,…”

“…Currently, 33 countries and regions have introduced the universal VarV since 2014 [19]. The effectiveness of the VarV was proven in many countries, and a dramatic decline in the incidence of varicella has been reported [5][6][7][8]20].…”

Letter to the Editor: Epidemiological Comments on the Effectiveness of the Varicella Vaccine in Korea

“…But it is questionable whether the exposure (vaccination) information in the control group of their previous study was representative of that in the population at risk where cases arose. For example, Choi et al 6 pointed out the problem as follows: “the vaccination rates in cases and controls were 76% and 78%, respectively, which was much lower than the results (> 95%) of the nationwide vaccination surveys.” Using the raw data from the authors' case-control study, 3 we have examined how the effectiveness of the varicella vaccine would have changed if the authors had used an alternative population-based (not patient-based) control group with a vaccination rate similar to the nationwide averages (i.e., ≥ 90%; 88.3%–91.7% in 2007 and 98.9% in 2012) around their study period. 2 12 Table 1 shows that while the crude effectiveness of the varicella vaccine is 12% when the vaccination rate in the control group is 78% as in the authors' previous study, it ranges from 65% to 90% when the vaccination rate in the alternative population-based control group increases from 90% to 97%.…”

“…The authors said that “In Korea - where one-dose of varicella vaccination for all children aged 12–15 months was recommended by the National Immunization Program (NIP) in 2005 … the incidence rate of varicella has been continuously rising from 22.4 per 100,000 persons to 154.8 from 2006 to 2017.” 1 Based on the varicella incidence statistics, the authors further said that “a universal one-dose varicella vaccination program may have limited effectiveness to decrease in the incidence rate of varicella …” However, we think that the authors should have cautiously used and interpreted the varicella incidence statistics because the statistics were based on the data from the National Notifiable Disease Surveillance System (NNDSS) in which only varicella cases notified by medical doctors and other responsible persons were included and counted. In fact, in contrast to the argument of the authors, utilizing more nationally representative data (i.e., the claims data from the National Health Insurance Review and Assessment Service [NHIRAS]), both Choi et al 6 and Jung et al 7 have demonstrated that the incidence rate of varicella has substantially decreased in Korea (e.g., from 5.71/1,000 person-years in 2004 to 1.87/1,000 person-years in 2015) after the introduction of the varicella NIP in 2005. Like Jung et al, 7 we think that the seemingly increasing incidence rate of varicella with the NNDSS data is a result of an improvement in doctors' reporting rate of national notifiable infectious diseases, 8 including varicella rather than an actual increase in varicella incidence during 2006–2017 in Korea.…”

Trends in varicella epidemiology before and after the implementation of universal one-dose varicella vaccination

“…Human vaccines & immunotherapeutics demonstrated that the incidence rate of varicella decreased 67% after universal one-dose varicella vaccination in South Korea. 1 Another cohort study by Cheng et al demonstrated that the incidence rate of varicella decreased 82.8% after universal one-dose varicella vaccination in Taiwan. 2 Some points needs to be discussed.…”