Response to recombinant yeast-derived hepatitis B vaccine in Arab infants

To determine the long-term (3 years) response to hepatitis B vaccine, 246 full-term healthy children, aged 10-44 months, who had been given three doses of Engerix B vaccine were studied. Children were divided into three groups by age at the time of the study: group I, 10-19 months (mean, 13.6 months) (n = 117); group II, 20-29 months (mean, 24.7 months) (n = 63), and group III, 30-44 months (mean, 37.7 months) (n = 62). The groups were compared for seroprotection rate by measuring the anti-HBs titers (Abbott Axsym System). Anti-HBs levels above the presumed protection limit were found in 96.6% of group I, 95.2% of group II and 83.8% of group III. The respective geometric mean titers (GMT) were 429.6, 185.7 and 186.5 mIU/ml. There was a significant difference in seroprotection between group I and II (p = 0.0001), group I and III (p < 0.0001), and group I and groups II and III combined (p < 0.0001). The specific response to the recombinant hepatitis B vaccine in this specific infant population was characterized by high immunogenicity with rates of nonresponse of 3.4-4.8% but with an early decline in antibody titer after 2 years of age. At a mean age of 35 months, 16.2% of the children had antibody levels below the presumed protection limit.