Increasing varicella incidence rates among children in the Republic of Korea: an age–period–cohort analysis

Abstract

In the Republic of Korea, despite the introduction of one-dose universal varicella vaccination in 2005 and achieving a high coverage rate of 98.9% in 2012, the incidence rate has been increased sevenfold. This study aimed to investigate time trends of varicella incidence rate, assessing the age, period and birth cohort effects. We used national data on the annual number of reported cases from 2006 to 2017. A log-linear Poisson regression model was used to estimate age–period–cohort effects on varicella incidence rate. From 2006 to 2017, the incidence of varicella increased from 22.5 cases to more than 154.8 cases per 100 000. Peak incidence has shifted from 4 to 6 years old. The estimated period and cohort effects showed significant upward patterns, with a linear increasing trend by net drift. There has been an increase in the incidence among the Korean population regarding period and cohort despite the universal vaccination of varicella vaccine. Our data suggest the need for additional studies to address the current gap in herd immunity.

Spatiotemporal Distribution of Varicella in South Korea

“…In our study, childhood percentage showed vulnerability to varicella outbreaks. This concurs with a previous study conducted APC analysis of varicella incidence in Korea [8], in which the peak incidence was 4-6 years of age. In a spatial analysis of mumps in Korea, childhood percentage was a signi cant risk factor for mumps because children are more susceptible than other age groups [9].…”

Letter to the Editor: Effectiveness of the Varicella Vaccine in Korea: Unresolved Issues

“…The vaccination rate for varicella vaccines in the case-control study during 2006–2007 was already above 90% (94% in the case group and 97% in the control group), which was considerably greater than 78% reported in the authors' case-control study in 2013. 3 In terms of the age distribution of study subjects, the case-control study 5 and the authors' case-control study were similar to each other. Thus, we stand by the results of our simulation analysis in our previous letter, supporting the possibility of a significant underestimation of the effectiveness of varicella vaccines in the authors' case-control study.…”

“…We deemed that the national varicella vaccination rate in Korea would be at least 90% in 2007 when most subjects of the authors' study in 2013 were not born or yet eligible for varicella vaccination (12–15 months old). It was based on the result in one nationwide case-control study 5 that had been conducted during 2007–2008 in 212 children (mean age: 5.2 years old; range from 1 year to 14 years). The vaccination rate for varicella vaccines in the case-control study during 2006–2007 was already above 90% (94% in the case group and 97% in the control group), which was considerably greater than 78% reported in the authors' case-control study in 2013.…”

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

“…Despite national programs to prevent and manage chickenpox, mumps, and scarlet fever, there were outbreaks of these infections in the pre-pandemic period. Indeed, although the vaccination rates for chickenpox and mumps have been increasing since the first implementation of vaccines at the beginning of the 20th century, there was an upward trend in incidences from 2006 to 2019 in South Korea [ 24 , 25 ]. Evidence from a previous study indicated that Suduvax, the most popular vaccine for chickenpox in South Korea, may be insufficiently immunogenic to prevent this disease [ 26 ].…”