ObjectiveTo evaluate the response to second vaccination series among post-booster sero-negative children who had previously received compulsory HBV vaccination. Subjects and methodsAfter given a booster dose to 1070 children, 103 of them failed to generate anamnestic response (anti-HBs <10IU/L). Only 91/103 children received additional two doses of recombinant HBV vaccine (i.e. 2nd vaccination series) after 1 and 6 months post-booster. Blood sample was withdrawn aseptically one month later for quantitative assessment of anti-HBs to detect development of protective immune response (≥10IU/L). Immunological vaccination failure was assigned to children who did not develop protective immune response after 2nd vaccination series. ResultsProtective immune response was detected among 84/91 children (92.3%). While 7/91 (7.7%) whose age were ≥10 years did not respond and had post-booster undetectable anti-HBs. About 80% of children with post-booster detectable anti-HBs showed significant protective immune response (anti-HBs ≥100IU/L) and higher GMT (299.1±3.6IU/L) compared to those with undetectable 60% and 106.2±12.9IU/L respectively (P<0.05). No significant difference was detected as regards gender or residence, P>0.05. All children with history of rheumatic fever (7 children) or diabetes mellitus (1 child) developed immune response after 2nd vaccination series. ConclusionA booster dose of HB vaccine may be unable to induce sufficient immunological response in children who had undetectable anti-HBs titers. Revaccination for non-responders is an important procedure to increase HBV protection rate.