Humoral and cell-mediated immune response to a new abbreviated regimen of purified vero cell rabies vaccine

Abstract

The 2-1-1 regimen, a new abbreviated regimen of' reduced cost ant rabies vaccination, consists of 2 I.M. injections of dose' each on day 0, followed by additional dose oh day 7 and 21. This regimen saves 2 doses of vaccine and 3 clinic visits, as compared to the conventional six dose. The immunogenicity of the 2-1-1 regimen of PVRV was evaluated in this study in patients after a low-risk exposure to rabies, in comparison to the full-dose I.M. PVRV (0.5 ml I.M. on day 0,3,7,14,28 and 90). In addition, the suppressive or interfering effect of human rabies immune globulin (HRIG) and equine rabies immune globulin (ERIG) when given with the 2-1-1 regimen was also studies. 78 patients were randomized into four groups to receive: (a) full-dose (0.5 ml) I.M. PVRV (N = 24) (b) 2-1-1 regimen (N = 22) (c) 2-1-1 PVRV + HRIG 20 IU/kg (N = 14) (d) 2-1-1 PVRV + ERIG 4 0 IU/kg (N = 17) Both HRIG and ERIG were given I.M. only once at buttock areas without local wound infiltration at the initiation of vaccination whereas PVRV was given at deltoid areas. Neutralizing antibody and specific cell-mediated immune response were sequentially followed up to day 180 and 90 respectively. All regimens resulted in 100% seroconversion by day 14, but 1 of the 17 patients in the 2-1-1 plus ERIG group had antibody lower than the arbitrary protective level of 0.5 iµ/ml. The 2-1-1 regimen had significantly higher antibody response than the full-dose I.M. on day 14 , but was significantly lower than the full-dose I.M. on day 180. No significant difference in seroconversion in both groups was observed on day 7. There was also no significant difference in the onset or the peak response of the antigen-specific CMIR in the 2-1-1 and the full-dose regimens. However, when HRIG or ERIG was simultaneously given with the 2-1--1 PVRV, significant suppression of the antibody response was observed. We therefore recommend that, for economical and immunogenicity reasons, the 2-1-1 regimen of PVRV should replace the full-dose intramuscular regimen in post-exposure prophylaxis where rabies immune globulin is not indicated. The suppressive effect of HRIG and ERIG on the 2-1-1 regimen of PVRV should be further studied in larger population.