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Bull World Health Organ. 1986;64(6):867-71.

Clinical trial of hepatitis B vaccine in a simplified immunization programme.



A study was conducted in the rural areas of Senegal to assess the immunogenic effect of 2 doses of hepatitis B vaccine with a 6-month interval followed by a booster dose after another month and to compare them with those obtained using 2 doses of a vaccine with a 2-month interval or 3 doses at 1-month intervals. The study population of infants received 3 injections of hepatitis B vaccine at 6-month intervals (T0, T6, and T12, respectively), with the 3rd dose as a booster. Other vaccines also were administered to subsets of children: BCG and diphtheria/tetanus/pertussis-polio (DTP-polio) at T0 and DTP-polio at T6 and T12. 664 infants received the 1st dose of hepatitis B vaccine, 409 the 2nd dose, and 177 the 3rd dose. Blood samples were taken at the time of each injection and in the case of 89 infants also 2 months after the last (booster) dose. Only 26.7% of the infants completed the entire series of injections. Only results from infants who were seronegative at T0 are presented, i.e., 281 infants at T6, 116 at T12, and 65 at T14. At T0 the mean age of the seronegative infants was 10.2 months and that of the seropositive infants with anti-HB antibodies was 7.4 months. The mean age of infants who were only anti-HBc-positive was 4.8 months and that of infants who were already HBsAg-positive at T0 was 14.3 months. The results were compared with those reported for 2 other groups of Senegalese infants: 72 seronegative infants who were immunized using a protocol of 2 doses of hepatitis B vaccine with a 2-month interval; and 111 seronegative infants immunized using 3 doses at 1-month intervals. Both groups also received a booster 12 months after the 1st dose. The anti-HBs response was determined 6 months after the T0 dose of hepatitis B vaccine for the 281 infants who were seronegative. 185 of these children (65.8%) exhibited anti-HB antibodies, but the geometric mean titre (GMT) was only 6.1 mlU/ml. The anti-HBs response of the 116 infants who received the 2nd dose of vaccine was determined when the 3rd (booster) injection was given (T12): 104 were positive for anti-HBs (89.7%), and the anti-HBs GMT was 83.7 mlU/ml. Assay of blood samples from 65 infants 2 months after the booster dose indicated that 62 (95.4%) had anti-HBs antibodies, the anti-HBs GMT reaching 348 mlU/ml. The study results establish that infants administered two 5-mcg doses of hepatitis B vaccine with a 6-month interval exhibit a seroconversion rate and antibody levels comparable to those produced using a protocol comprising 2 doses with a 2-month interval or 3 doses at 1-month intervals.

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