Zhao YL, et al. - In order to estimate the immune persistence conferred by a Chinese hamster ovary (CHO)-derived hepatitis B vaccine (HepB) 17 to 20 years following primary immunization during early life, researchers measured hepatitis B surface antibody (anti-HBs), surface antigen and core antibody levels in blood samples of participants born between 1997 and 1999 who received a full course of primary vaccination with HepB (CHO) and who had no experience with booster vaccination. Among a total of 1,352 participants, an anti-HBs antibody ≥10 mIU/mL was retained in 1,007 (74.5%) participants. Six participants had HBsAg, indicating an HBsAg carrier rate of 0.4% (6/1,352). Since primary vaccination administered 17–20 years ago conferred satisfactory immune protection against HBV infection, no urgent need for booster immunization was suggested.