Adjuvant effect of DEAE-dextran and tetanus toxoid on whole cell heat inactivated phenol preserved typhoid vaccine.

Active mouse protection test (AMPT) and enzyme linked immunosorbent assay (ELISA) were used to determine the immunogenicity of whole cell typhoid vaccine when administered in conjunction with either tetanus toxoid (TT) or DEAE-Dextran (DD). Immunization of mice with whole cell typhoid vaccine showed enhanced potency either when administered in conjunction with TT or DD and values were statistically significant (p < 0.05) in comparison to conventional or standard typhoid vaccines. For ELISA, the mice were immunized with 2 different schedules, one in which a single dose of 0.25 ml subcutaneously (s/c) was administered and in another two doses of 0.25 ml each s/c, 14 days apart. In case of single dose schedule of immunization D vaccine (Whole cell typhoid + 5 mg/ml DD) showed significant increase of immune response (3.201 log10) as compared to plain vaccine (2.550 log10). Two dose schedule further increased the titres to 3.856 log10. DD adjuvanted vaccine showed higher potency by AMPT as compared to the TT adjuvanted vaccine or plain vaccine. The present study clearly demonstrates that a single dose of 0.25 ml which is equivalent to half of the conventionally used single human dose of typhoid vaccine adjuvanted with DD can significantly improve the immunogenicity of the vaccine.