At the time of the present study, the necessity for booster vaccinations for the prevention of hepatitis B(HB) 15 years post-vaccination in the group of young adults who have become seronegative for HB markers after complete neonatal HB vaccination was in question. A booster vaccination strategy may lead to a significant economic impact on national health care resources, and the costs/benefits must therefore be carefully evaluated. Unfortunately, the data to support such analyses are lacking. Because an increased risk of HB infection is anticipated when adolescents enter into young adulthood through becoming sexual active, breakthrough infections such as fulminant HB might be the main concern instead of the risk of chronic HB carriage. To address this issue, this study aimed to measure the booster responses after HB vaccination in seronegative young adults who had completed neonatal HB vaccines in Taiwan before.

This cohort study was conducted between October 2007 and Jan 2009. The target population was subjects aged 18-23 years who were born after 1984 when the Taiwanese national HB vaccination program was launched. Their vaccination records must have shown a completed neonatal HB vaccination, and they were seronegative for all three HB viral markers including HBsAg(Hepatitis B surface antigen), anti-HBc(core antibody against Hepatitis B), and anti-HBs(Surface antibody against Hepatitis B) within 2 years of entry into the study and at study entry. They were recruited through a Student's Health Center Clinic referral, Bulletin Board System posts, and Web-broadcast invitation. The neonatal HB vaccination records were verified through linkage to the Taiwan Center for Disease Control databank. Signed informed consent was obtained from all the participants and their parents or guardians. Pregnant females, persons with a previous history of allergy to HB vaccines, or allergy to yeast were excluded. First 3 months are screen phase to recruit college students for assay of hepatitis B viral markers. Seronegative subjects were approached for enrollment into receiving hepatitis B vaccine booster afterwards.

All participants were tested for HB markers at enrollment, even if they had been tested in the previous months, to confirm their status. A questionnaire was completed at enrolment to record sociodemographic factors including age, gender, self reported family history of hepatitis B carriers, self reported blood type, and so on. The participants then received three intramuscular doses of HB vaccine (Engerix-B, recombinant hepatitis B surface antigen, 20 microgram/ml/vial, GlaxoSmithKline, Belgium) at baseline and at the 1st and 6th month follow-up visits. Their anti-HBs status was checked at baseline, 7-10 days, 1 month, 6 months, and 7 months following the first dose of HB vaccine. Adverse effects associated with the vaccine were also reported within one week after each Engerix-B injection.

Inclusion Criteria:

1. aged 18-23 years
2. the youth born after July 1984 who have received a hepatitis B virus markers checkup within 2 years including HBsAg, core antibody against hepatitis B(anti-HBc), and surface antibody against hepatitis B (anti-HBs) and the results are all negative for these 3 viral markers.
3. Participants should agree to sign inform consent. For younger than 20 years old subjects, one of their parents also help the participate review and sign the inform consent.
4. Participants are willing to receive 3 doses of Hepatitis B vaccines without payment.
5. General condition is in good health judged by the doctor

Exclusion Criteria:

1. Allergy to Hepatitis B vaccines or yeast
2. pregnancy

The possible presence of T cell memory among the seronegative patients for HBsAg(+), anti-HBc(+), and anti-HBs(+) could be a concern.