[Seven-year follow-up in pupils immunized with hepatitis B vaccine and its revaccination].

In order to evaluate immune persistence of plasma-derived hepatitis B vaccine (HBV), 344 children in a primary school were followed up for seven years by detection of serum HBsAg, anti-HBc and anti-HBs with radioimmunoassay (RIA) using Abbott reagent kits. In the seventh year after three-dose HBV immunization, level of anti-HBs in 55.4%-75.0% of the vaccinee was greater than 10 IU/L, with a geometric mean titer (GMT) of 20.9-65.3 IU/L. The higher the level of anti-HBs, the longer the duration of its decrease from more than to less than 10 IU/L. Seven years after immunization, 66 children with varied serum levels of anti-HBs were received a fourth dose of 10 micrograms HBV, and one month after revaccination, their levels of anti-HBs increased by 6.3-57.7 times. It suggests revaccination of HBV is not necessary for children vaccinated within seven years.