Evaluation of the immune response to Hepatitis B vaccine in different age groups of the population of Sana'a - Yemen

The study was made to evaluate the immune response to HBV among individuals with different ages and sexes by measuring the level of circulating anti-HBs antibodies over an interval of 1 to 5 years after immunization with the three doses of hepatitis B vaccine. A total of 300 individuals vaccinated against HBV prior to the study were included, of whom males represent 47.7% and females 52.3% with a mean age of 26.67 years. Sera were tested for HBsAg and anti-HBc by qualitative ELISA and anti-HBs by ELISA quantitative technique.The individual's data were collected in a pie-designed questionnaire including: vaccination date, number of doses of vaccine, sex, occupation and age at the time of the present study. Two hundred and sixteen [81.2%] of 266 individuals [lacking both HBsAg and anti-HBc] responded to the vaccine with anti-HBs antibody level >/= mlu/ml. Thirty-four [11.3] of 300 individuals wre reactive to anti-HBc, indicating an immune response due to previous infection rather than vaccination. Seven [2.3%] of all vaccinated individuals were reactive to HBsAg, indicating infection, Individuals having ages < 15 years had the highest immune response [89.8%] with antibody level >/= 10mlu/ml. There was no difference in response at ages from 16-35 [82.8%], while the lowest response was obtained at ages >36 years [66.7%]. The present study included two vaccination schedules, the first one at 0,1,2 months, showing an immune response of 62.2%, while the second schedule at 0,1,6 months showed a greater immune response of 83.1%. Individuals immunized with a yeast-derived vaccine had higher anti-HB5 levels [81.9%], than those immunized with a plasma-derived vaccine [79.8%].The year intervals [1-5 years] after primary immunization showed no difference in the immune response. This study revealed a high response rate to the vaccine. However, a considerable proportion of vaccinated individuals remain to be reconsidered for either revaccination or booster doses due to nonexistent, inadequate, or low response. The schedule of 0, 1, and 6 months was more efficient in inducing antibodies towards the vaccine than the 0, 1, 2 months schedule