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Abstract
Background: In a campaign to vaccinate health care workers, a three-dose schedule (0, 1, and 6 months) and a four-dose schedule (0, 1, 2, and 14 months) with hepatitis B (HB) vaccine were used. After primary immunization 26 subjects vaccinated with the 3-dose schedule and 4 subjects vaccinated with the 4-dose schedule had undetectable anti-HBs titres. Methods: All these 30 non-responders received an extra dose of the same vaccine 2 months after primary immunization and a booster dose with a yeast-derived vaccine 6 years later. Anti-HBs levels were evaluated 1 month after the extra dose and after the booster dose. Results: One month after the extra dose 26.9% (7 of 26) of the subjects vaccinated with the 3-dose schedule became positive for anti-HBs. Six years later only two of these subjects had detectable anti-HBs. After the booster dose the seven subjects who responded to the extra dose showed an anamnestic type of response, and five additional subjects became positive for anti-HBs. Responders to the extra dose were significantly younger than the non-responders. In the four-dose group only one subject responded to the extra dose, and that subject maintained protective anti-HBs. Conclusion: About 25% of non-responders to primary HB vaccination could benefit from an extra dose, and these subjects show an anamnestic type of response to HBs antigen even after 6 years. This response seems to be influenced by age.