OBJECTIVEThe aim of the study was to evaluate the anti-HBs persistence and the long term preventive efficacy after vaccination 23 years with plasma-derived hepatitis B vaccine.

METHODSThe study consisted of 261 children who were 5 - 9 years aged, from two primary schools in two townships of Xi'an. 126 children were randomly selected as vaccine group, and 135 children in control group. These children were followed up again in 2009. Excluding self-inoculation, the vaccine and control groups were 81 and 75, who was used to ask to recall details of their experience for vaccination and liver-related illnesses during past twelve years. Individuals who had anti-HBs titers less 10 mIU/ml, HBsAg, anti-HBc and HBV-DNA all were negative, were given a booster dose vaccine and retest for anti-HBs titer after one month.

RESULTSAfter eliminated the interference of an early booster dose and vaccination outside the study, the positive rate of anti-HBs was 48.1% (39/81) in the vaccine group at year 23, higher than 34.7% (26/75) in control group. At year 23 after primary vaccination, 84.0% (21/25) individuals in the vaccine group whose anti-HBs and anti-HBc both are negative showed a stronger anamnestic response after received a booster dose, while 7.5% (3/40) in the control group. At year 23 after primary vaccination, none clinical case of hepatitis B was found among 194 individuals. However, anti-HBc positive rate in the vaccine group was 16.0% (13/81), while the rate in the control group was 30.7% (23/75) (χ(2) = 4.687, P < 0.05).

CONCLUSIONAt 23 years after implemented a full course of plasma-derived hepatitis B vaccine, the recipients of vaccine were maintained anti-HBs at a high level or strong immunological memory.