Hepatitis A vaccination by intracutaneous low dose administration: a less expensive alternative.

We investigated the immune response to three different intracutaneous (i.c.) doses of inactivated hepatitis A vaccine: 72, 144, and 216 ELISA units (EU). The response was measured using a quotient score derived from a commercial enzyme-linked immunosorbent assay (HAVAB Abbott) and translated to IU per liter using a World Health Organization standard serum for hepatitis A virus antibody. The results were compared with the results obtained after an intramuscular (i.m.) full dose, i.e. 1,440 EU, at 0 and 6-12 months. As estimated from antibody concentration, 3 lots of 144 EU i.c. with 100% or two lots of 216 EU i.c. with 98% seroconversion results in at least as good early protection as the standard immunization with one lot of 1,440 EU i.m., (79% with our method). Indeed, only two doses of 144 EU vaccine (90% seroconversion) seem to give results comparable to the standard procedure. After the booster dose the median antibody concentration is 1,290 IU/l for the 144 EU vaccine and 837 for the 216 EU one, compared with an antibody response of 990 IU/l for the standard 1,440 EU i.m. vaccination. In conclusion, three doses of 144 EU vaccine i.c. or, as an alternative, two doses of 216 EU at monthly intervals give good early protection (e.g. before travel). After the booster dose, which is given 6 months to 1 year later, the serological response is comparable to the standard procedure of two doses of the 1,440 EU vaccine given i.m. and with 100% seroconversion in all three programs.