RESPONSE TO A BOOSTER DOSE 18 MONTHS AFTER A LOW ANTI-HBS RESPONSE (10-99 IU I) TO 3 DOSES OF INTRADERMALLY OR INTRAMUSCULARLY ADMINISTEREDRECOMBINANT HEPATITIS-B VACCINE/

The response to a booster dose, given by the same route 18 months afte r the completion of the primary vaccination scheme, was studied in hos pital 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 administ ered at 0, 1 and 6 months. At the time of boostering the anti-HBs leve ls had declined to < 10 IU/l in 44/51 (86%) of the i.d. and 10/11 of t he i.m. vaccinees. All i.m. and 90% of i.d. vaccinees responded to the booster dose with anti-HBs level greater than or equal to 10 IU/l, an d with geometric 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 (amo ng whom the anti-HBs levels in the majority had declined < 10 IU/l) mo unted an anti-HBs level greater than or equal to 10 IU/l after a boost er dose. The anti-HBs concentrations were generally higher after i.m. than i.d. booster doses in accordance with the response to primary vac cination.