How long is hepatitis B vaccine protective?

Studies indicate that immunologic memory remains intact for at least 30 years and confers protection against clinical illness and chronic HBV infection, even though anti-HBs levels that once measured adequate might become low or decline below detectable levels. If exposed to HBV, people whose immune systems are competent will mount an anamnestic response and develop protective anti-HBs. Studies are on-going to assess whether booster doses of HepB will be needed in the future.