Hepatitis B virus (HBV) infection is a major public health problem worldwide and HB vaccine is the most effective measure to prevent HB virus infection. An initial anti-HBs threshold value of 10 mIU/ml or greater is considered generally protective. However, the protective antibodies induced by HB vaccine wane gradually over time and may reach very low or even undetectable level. Immunologic studies indicated that HB vaccine induces immunologic memory and memory B cells can generate a rapid and vigorous anamnestic anti-HBs response upon re-exposure to HBsAg. Accordingly, long-term protection after vaccination and the possible need for booster dose of vaccine has remained controversial. To answer this question, we used two different approaches to determine the duration of protection provided by HB vaccine. Four different studies will be presented: a) Seroprotection of HB vaccine and need for booster dose: A meta-analysis b) Long-term protection provided by HB vaccine ...