KRT88P and hepatitis A virus infection: • Healthy adult aged 40–80 years• No history of hepatitis B disease• No prior receipt of any hepatitis B-containing vaccine• Undetectable level of anti-HBs and anti-HBV core (HBc) antibody and HBs antigen at study enrolment• Generally good health (stable chronic conditions acceptable)• Living independently or with minimal assistance (clinical frailty score 1–5)78 and able to attend all study visits• Willing and able to comply with the requirements of the protocol• Provided informed consent for participation in the study