Effect of age on the incidence of acute hepatitis B after 25 years of a universal newborn hepatitis B immunization program in Taiwan.

Background: Raising concerns about the waning immunity of cohorts receiving hepatitis B virus (HBV) vaccination in infancy persuaded us to identify the changing incidence of acute hepatitis B (AHB) in children and young adults.
Methods: Data on AHB surveillance through the National Notifiable Disease Surveillance System from July 2001 to June 2009 were collected and described. Cases were divided into 2 cohorts according to their birth year: before or after the universal newborn HBV vaccination program. Age-specific incidence was compared for the 2 birth cohorts with diagnosis at age 15-24 years.
Results: In total, 2226 patients with AHB were identified. AHB rates varied by age; the highest rates occurred among unvaccinated individuals aged 25-39 years (2.33/100 000). Due to breakthrough HBV infection from mother-to-infant transmission, vaccinated infants (0.78/100 000) had higher rates than those aged 1-14 years (0.04/100 000), who had the lowest rates. The incidence in vaccinated birth cohorts was significantly lower than in unvaccinated birth cohorts among patients 15-24 years old, with an adjusted-relative risk of 0.42.
Conclusions: Implementation of universal-at-birth HBV immunization programs has effectively reduced the occurrence of AHB among adolescents and young adults in Taiwan for >25 years, making infants and the 25-39-year-old cohort additional targets for preventing AHB.