Long-term efficacy of plasma-derived hepatitis B vaccine: a 15-year follow-up study among Chinese children
Introduction
The immunogenicity and short- and medium-term protective efficacy of the hepatitis B vaccine have been well documented [1], [2], [3], [4], [5], [6], [7], [8]. However, the duration of protection is still unknown, especially when antibody against hepatitis B surface antigen (anti-HBs) declines to low or undetectable levels. Levels of anti-HBs increase rapidly when vaccine recipients are exposed to hepatitis B virus (HBV) or receive a booster dose of vaccine [9], [10]; however, the necessity and timing of booster doses of vaccine need to be established [10]. To address these gaps in our knowledge and to observe long-term vaccine efficacy and changes in serologic markers after vaccination, we have conducted follow-up examination of children from Longan county, Guangxi province, China who participated a randomized, double-blind and placebo-controlled trial on a pre-market plasma-derived hepatitis B vaccine in 1982. In this paper, we report serologic changes in HBV markers and vaccine efficacy 15 years after the initial vaccination in 649 children recruited in 1982.
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Immunization procedures
Between October 1981 and April 1982, 966 children, ranging in age from three to thirty-six months (mean age, 16 months), were recruited from vaccination-clinics at seven towns in Longan county, Guangxi province, China, an endemic area for HBV infections. Participants at each clinic were randomly allocated into vaccine (n=477) or control (n=489) groups. The two groups were comparable in age and sex. The group allocation was unknown to the parents of the children and the staff. Children in the
Characteristics of the cohort
Demographic characteristics of the vaccinated and the control groups were similar. The mean age of 649 participants at the first dose of vaccine/placebo was about 14.3 months in the vaccinated and 14.6 months in the control group. Proportions of boy were 56% (171/308) in the vaccinated and 53% (180/341) in the control group. No significant difference in distribution of towns of residence was found between the vaccinated and control groups at each observation.
Levels of anti-HBS during the 15 years
Fig. 1 shows changes in proportions
Discussion
We found in this study that protective efficacy against HBsAg at 15 years after vaccination was about 89% and the efficacy against chronic HBsAg carriage was 96%. After vaccination, the level of anti-HBs increased rapidly in vaccinated children at 6 months after vaccination, then decreased substantially. Other investigators in China [4], [7] have reported a similar pattern of decreased levels of anti-HBs. However, in the studies of Wainwright et al. [3] and Coursaget et al. [6] the decrease in
Acknowledgements
This study was supported by grant from China Medical Board in the United States (Grant No. 93-582).
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