Low rates of seroconversion after hepatitis B vaccination in orphanges with high prevalence of virus carriers.

A serosurvey of Hepatitis B infection markers was conducted in two orphanages that adhered to Hepatitis B vaccination policy. In spite of comparable sizes (80-90 children per facility), housing conditions and infection control practices, the level of HbsAg endemicity was different in each unit in direct relation with the mean age of the children. The prevalence of HbsAg carriers and the interval spent in collectivity strongly affect the seroconversion rate after HB vaccination. Other elements that can explain the low seroconversion rate were: the proportion on fully vaccinated children, the number of vaccine administered doses and the delayed age at which childhood immunization schedule was initiated. In order to increase the protective antibody response, booster doses were administered to a limited number of nonseroconvertors or to children with a nonprotective level of anti-HBs antibody (< 10 UI). This intervention provides evidence of prompt rising in antibody titers, comparable with titers found in children with wild infection.

Study of specific immune response to unadsorbed concentrated tetanus vaccine administered by intradermal route to non-immunized persons in the last ten years.

Investigations of anti-tetanus response, in 404 subjects, most of them aged 60, being non-immunized for at least 10 years, stressed out the fact that 28.7% were not protected and 6.18% presented a protecting titer of 0.01 IU/ml, evaluated by "in vivo" protection test in mice. Some subjects were immunized with unadsorbed Tetanus vaccine (10 Lf/0.1 ml/dose) by i.d. route, using Jet-injector, and the others with adsorbed Tetanus vaccine (0.5 ml/dose), by i.m. route, using the needle and syringe. The vaccines were well tolerated and adverse reactions were not recorded. After 30 days, a single vaccine dose produced a protecting effect in 97.45% of non-protected subjects, belonging to i.d. immunized group, and also in 93.33% belonging to i.m. immunized group. 30 days after the administration of a second dose, protection set up in all subjects, no matter of vaccine type and administration route used. For a continuous reduction of tetanus morbidity, the authors suggest a specific periodical immunization of non-protected persons, selected by serological screening, using unadsorbed Tetanus vaccine, administered by i.d. route by means of the Jet-injector.