1 Understand that hepatitis B vaccination-induced protective antibodies can last for up to 15 years, but appear to fall off over time.2  Patients who were vaccinated 10 to 15 years ago, especially those who were vaccinated as children, may not be adequately protected. Patients who were vaccinated 10 to 15 years ago, especially those who were vaccinated as children, may not be adequately protected. 2  For patients with this history who are at moderate to high risk of hepatitis B infection consider quantitative hepatitis B antibody measurement to determine protective immunity.