Intramuscular versus low-dose intradermal hepatitis B vaccine. Assessment by humoral and cellular immune response to hepatitis B surface antigen.

The capacity of hepatitis B surface antigen (HBsAg) vaccine (which was administered by the conventional intramuscular route or as a one-tenth dose by the intradermal route) to elicit an antibody or delayed-type hypersensitivity response to HBsAg was compared for 40 paired healthy subjects, 20 per group, of whom 38 completed the vaccination protocol. The 40 subjects were allocated at random to receive three doses of 20 micrograms of vaccine intramuscularly, or three doses of 2 micrograms of vaccine intradermally. Titres of antibody to HBsAg (anti-HBs) were expressed in a radioimmunoassay by sample ratio (signal-to-noise) units (SRU). The maximal mean levels of anti-HBs (maximal one month after the third injection) were 108 SRU for the intramuscular group and 51 SRU for the intradermal group, and the levels for the intramuscular group were significantly higher at all other time-points. The levels of anti-HBs declined equally with time over 18 months in both groups. More subjects in the intramuscular group (17 of 19 subjects) showed a response to anti-HBs than in the intradermal group (14 of 19 subjects). Non-respondents in either group responded with similar frequency to further intramuscularly-administered vaccine. The frequency of delayed-type hypersensitivity to HBsAg was similar for both groups. Thus, immunization with HBsAg, when administered intradermally in a dose that is one-tenth of that recommended for intramuscular administration, induces an immune response in healthy subjects. However, since the level of antibody is lower than that after intramuscular injection, revaccination might be needed at more frequent intervals.