Response to a booster dose 18 months after a low anti-HBs response (10-99 IU/l) to three doses of intradermally or intramuscularly administered recombinant hepatitis B vaccine.

The response to a booster dose, given by the same route 18 months after the completion of the primary vaccination scheme, was studied in hospital staff members who responded with anti-HBs levels in the range of 10-99 IU/l after three intradermal (i.d., n = 51) or intramuscular (i.m., n = 11) doses of recombinant hepatitis B virus (HBV) vaccine administered at 0, 1 and 6 months. At the time of boostering the anti-HBs levels had declined to < 10 IU/l in 44/51 (86%) of the i.d. and 10/11 of the i.m. vaccines. All i.m. and 90% of i.d. vaccinees responded to the booster dose with anti-HBs level > or = 10 IU/l, and with geonmetric mean titres 1,074 IU/l and 121 IU/l, respectively. It was concluded that all i.m. and 90% of i.d. vaccinees with an initial anti-HBs response of 10-99 IU/l after three doses of HBV vaccine (among whom the anti-HBs levels in the majority had declined < 10 IU/l) mounted an anti-HBs level > or = 10 IU/l after a booster dose. The anti-HBs concentrations were generally higher after i.m. than i.d. booster doses in accordance with the response to primary vaccination.