Evaluation of a reduced dose of hepatitis B vaccine administered intradermally.

Intradermal inoculation of hepatitis B vaccine (HBsAg subtype adw) caused no side effects, but the vaccine was less immunogenic than following intramuscular administration. Intradermal inoculation does not, therefore, offer a major advantage to the generally used intramuscular immunization. A single multisite intradermal administration of a reduced dose of vaccine did not result in a more rapid seroconversion compared to intramuscular inoculation. Although the antibody levels were similar after two intradermal or intradermal or intramuscular injections given 1 month apart, the booster (third injection) at 6 months resulted in anti-HBs levels that were about 10 times higher following intramuscular inoculation as compared to intradermal. All persons immunized developed anti-HBs. The levels of anti-HBs (a and w) were about 30-40% of the total anti-HBs, and the proportion did not change significantly during the course of immunization. Cross-protection against all HBV strains is thus also assured after intradermal administration of vaccine containing only one HBsAg subtype (adw). A skin reaction was elicited only in a small proportion of anti-HBs-positive individuals, and the reaction correlated roughly with the immune responses.