BACKGROUND: Hepatitis B vaccine confers long-term protection, and anti-HBs titre is a marker for protective immune response. The evaluation of immune status following vaccination is important in susceptible individuals as up to 10% immunised individuals tend to be non-responders who continue to be at risk of acquiring hepatitis B. AIM: The aim of the study was to determine the immune response and persistence of protective antibody levels after basic course of hepatitis B vaccination in susceptible individuals and to determine the factors affecting it. MATERIALS AND METHODS: A cross-sectional study on 400 susceptible participants who were tested for anti-HBs by quantitative ELISA at a tertiary care centre in North Kerala for a period of 1 year. The study population included healthcare workers and medical students divided into Category I: those vaccinated with 0-1-6 schedule within the past six months and Category II: beyond six months but within 10 years. Individuals who have taken booster doses were excluded from the study. RESULTS: 97.75% showed adequate anti-HBs levels (≥10 mIU/ml) after basic course of immunisation. Category I showed 99% response and Category II showed 96.5%. On giving one additional booster, the remaining 2.25% also responded. No non-responders were detected. 80.4% participants in the 10–20 age group showed anti-HBs >1000 mIU/ml, whereas only 25% participants in the 51–60 age group showed such high response. 97.9% males and 97.7% females had adequate response. Diabetic patients (66.7% vs. 98%) and smokers (66.7% vs. 98.2%) had a lower response (P < 0.001). CONCLUSION: Protective immune response was achieved in all participants after an additional dose in indicated individuals. There is a decline in antibody levels with time, but a good immunological memory persists up to 10 years after vaccination. Vaccine response is adversely affected by advancing age, smoking and diabetes.