This prospective cohort study aims to provide the evidence-based clinical guide to help decide the revaccination doses of hepatitis B vaccine that the high-risk young adults without hepatitis B seroprotective antibodies (anti-HBs titer<10 mIU/mL) need to take.

Purpose For young adults born after the neonatal hepatitis B immunization program, especially those who were 20-33 years old after 1987, additional hepatitis B vaccination may have the benefit of strengthening protection from acute hepatitis B infection among high-risk groups. However, how many doses are most appropriate for the protection of high-risk groups is still an issue to be resolved. This study aims to provide the evidence-based clinical guide to help decide the revaccination doses of hepatitis B vaccine that the high-risk young adults without hepatitis B seroprotective antibodies (anti-HBs titer<10 mIU/mL) need to take.

Materials and Methods From August 2021 to July 2024, the investigator will invite young adults born in Taiwan over the age of 20 and born after 1987, who have received a full course of hepatitis B vaccine at least three doses at their infant period. Those who are all negative for hepatitis B surface antibodies (anti-HBs) and surface antigens (HBsAg) are enrolled to 4 groups according to the anti-HBs titer concentration (anti-HBs titer between 2.5-10 mIU/mL is a low concentration, anti-HB titer less than 2.5 mIU/mL is an extreme low concentration) with one or two doses of hepatitis B vaccine (Engerix-B) administered, respectively. Each group recruits 60 cases to reach a total of 240 participants. Each participant was followed for 12 months, and the anti-HBs titer concentration was measured in 0, 7-10 days, 28 days, 24- 28 weeks, and 48-52 weeks. The investigator will calculate the anti-HBs titer reaction rate and immune response after receiving hepatitis B vaccine(s) at each stage, and do further univariate and multivariate analysis.

Expected Results This prospective cohort study can help understand the difference in the anti-HBs titer response after 1 or 2 revaccination doses by the anti-HBs titer concentration as well as the two different types of hepatitis B vaccination in childhood It is expected to provide an important reference for the administration of hepatitis B vaccine in young adults of high-risk groups.

Inclusion Criteria:

1. The actual age at the time of admission was higher than 20 years old and birth year after 1987
2. Born in Taiwan and had received a full course of hepatitis B vaccines at least three doses at infant period.
3. Those who have tested negative for hepatitis B surface antibody and surface antigen at baseline
4. Have never been vaccinated against hepatitis B in childhood and adolescence by questionnaire
5. Consent to administer 1-2 doses of hepatitis B vaccine according to the assigned group after sharing decision making process
6. In good health

Exclusion Criteria:

1. Those who were previously allergic to hepatitis B vaccine or its components (such as yeast)
2. Those who have been vaccinated against hepatitis B during childhood and adolescence
3. Those who have a positive test for hepatitis B surface antibody or a positive test for hepatitis B surface antigen