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.
Highlights
Varicella is an acute infectious disease caused by the varicella-zoster virus
An increasing tendency of higher varicella incidence rates with later periods was determined for each age group (Fig. 2a)
Despite the implementation of the universal varicella vaccination programme in July 2005, there was an increase in the incidence rate of varicella between 2006 and 2017 in Korea
Summary
Varicella is an acute infectious disease caused by the varicella-zoster virus It is highly communicable, with secondary attack rates >90% among susceptible individuals [1, 2]. The varicella vaccine, which became available in the early 1980s, conferred excellent immunogenicity against varicella infection. Countries such as the USA, Germany and Taiwan which adopted varicella vaccination programme experienced a reduction in the incidence rate of varicella [3,4,5]. Imported and domestic live attenuated vaccines are available in Korea. The former is based on Oka strain and used widely in many countries and the latter is based on MAV strain which is isolated from a Korean boy and is predominantly used in Korea. The incidence rate of varicella has yet to decline and, has been continuously rising, from 22.5 per 100 000 persons in 2006, to 154.8 in 2017 [6], despite the vaccine coverage reaching up to 98.9% in 2012 [7]
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