The chronological changes in the seroprevalence of anti-hepatitis A virus IgG from 2005 to 2019: Experience at four centers in the capital area of South Korea.

Although universal vaccination has been administered to toddlers, South Korea has had periodic nationwide outbreaks of acute hepatitis A since the late 2000s. We examined the chronological changes in the seroprevalence of anti-hepatitis A virus (HAV) immunoglobulin G (IgG) over the past 15 years (2005-2019). We retrospectively collected data from 45,632 subjects who underwent anti-HAV IgG testing without evidence of acute HAV infection at four centers in the capital area of South Korea between January 2005 and December 2019. The seroprevalence of anti-HAV IgG was analyzed according to age and compared among seven age groups and five time periods. Additionally, age-period-cohort analyses were used to identify the age, period, and cohort effects of the seroprevalence of anti-HAV IgG. The mean age of the enrolled subjects was 39.2 ± 19.2 years, and the average anti-HAV IgG positivity rate was 66.4%. During the 15 years, the seroprevalence of anti-HAV IgG in people aged 0 to 19 years significantly increased over time (P < .001). In people aged 20 to 29 years, the seroprevalence slightly decreased to that of the early 2010s (31.3% in 2005-2007 to 19.7% in 2011-2013) but rebounded to 39.5% in 2017 to 2019. In contrast, the seroprevalence of anti-HAV IgG in those aged 30 to 49 years decreased over time (P < .001). The seroprevalence of anti-HAV IgG in those aged 20 to 39 years in 2017 to 2019 was still less than 40%. In addition, the seroprevalence of anti-HAV IgG in people aged 50 to 59 years has recently decreased. Since the introduction of the universal vaccination, the seroprevalence of anti-HAV IgG in children and young adults has gradually increased. However, the seroprevalence of anti-HAV IgG in people in their 20s remains low, and the seroprevalence of anti-HAV IgG in people in their 30s and 40s is gradually decreasing. Therefore, a new strategy for HAV vaccination is needed for those in their 20s to 40s.