Abstract
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.
Highlights
Varicella zoster virus (VZV) causes varicella, which is a highly contagious disease in children with primary infection
A live-attenuated vaccine for varicella has been selectively used in Korea since 1988, and it has been included in the National Immunization Program (NIP) in Korea since 2005 for children aged 12–15 months with a single dose schedule [4]
Vaccinations involved four different vaccines; SuduVax (62.2%), Varilrix (10.7%) (GSK, Brentford, UK), Vari-L (1.1%) (Changchun Institute of Biological Products, Changchun-si, China), CJ Sudu vaccine (0.2%) (Cheil Jedang, Seoul, South Korea), and unknown vaccines accounted for 25.7% of the cases
Summary
Varicella zoster virus (VZV) causes varicella (chickenpox), which is a highly contagious disease in children with primary infection. A live-attenuated vaccine for varicella has been selectively used in Korea since 1988, and it has been included in the National Immunization Program (NIP) in Korea since 2005 for children aged 12–15 months with a single dose schedule [4]. The varicella vaccine coverage rates for children aged 6 years or less in Korea were 88.3%, 96.8%, and 99.0% in 2007, 2008, and 2009, respectively, and they were over 97% between 2016 and 2019 [5,6,7,8]. Varicella outbreaks occasionally occur in day-care centers or primary schools, even among vaccinated children with mild clinical presentation [9]. It is necessary to evaluate the immune status of the most vulnerable age groups to investigate the basis of varicella outbreaks
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