Evaluation of the Potency of the Pertussis Vaccine in Experimental Infection Model with Bordetella pertussis: Study of the Case of the Pertussis Vaccine Used in the Expanded Vaccination Program in Algeria

Abstract

In Algeria, vaccination against pertussis is carried out using the whole-cell pertussis vaccine combined with the diphtheria and tetanus toxoids (DTwp). The quality control of vaccines locally produced or imported is carried out before the batch release. The aim of our work was to evaluate the potency of pertussis vaccines. In the present study, five consecutive trials of potency were conducted on samples of the same batch of (DTwp) using the mouse protection test (MPT) against experimental infection of Bordetella pertussis strain 18323, based on the Kendrick test. The virulence of B. pertussis strain 18-323 was verified by the mortality of mice, with an average LD50 of 338.92, as well as the dose of the lethal test containing a mean number of LD50 of 324.43. The (MPT) test recorded a relative potency of 8.02 IU/human dose, with 95% CL of (3.56-18.05) IU/human dose. The development of the (MPT) at the laboratory of quality control of vaccines and sera at the Pasteur Institute of Algeria was effective in evaluating the potency of whole-cell pertussis vaccines. Interestingly, our study indicates that this potency is necessary for the vaccine quality assurance. Further validation is needed to strengthen the application and routine use of the test.

Keywords: Algeria; Bordetella pertussis; Kendrick test; LD50; relative potency; whole-cell pertussis vaccine.

Figure 1

The mouse protection test steps (MPT) (Kendrick test): (1) Day 0: immunization of one group of 24 mice by one dilution, simultaneously with a whole-cell pertussis vaccine combined with diphtheria and tetanus antigens (DTP) and a standard pertussis vaccine (three dilutions/vaccine, 0.5 mL, intraperitoneally), Plus a negative control (N.control) of 10 non-immunized miceinjected with diluent vaccine. (2) Day 14: challenge test with a suspension of B. pertussis of all groups of mice (0.03 mL, Intracerebrally), plus a control group of non-immunized mice infected with B. pertussis (LD50 estimation). (3) Day 28: final reading and recording of surviving mice to estimate the potency relative to the pertussis vaccine tested (Probit analysis).

Figure 2

Estimation of dose response regression lines of the pertussis component of DTP vaccine test and reference pertussis vaccine (RWSO1/11) by the parallel line method using WHO combistats software(dose response regression curves of the proportion of surviving mice transformed to a probit as a function of the dose): (A)The pertussis component of DTP vaccine test 1 and reference pertussis vaccine (RWSO1/11),(B) the pertussis component of DTP vaccine test 2 and reference pertussis vaccine (RWSO1/11),(C) the pertussis component of DTP vaccine test 3 and reference pertussis vaccine (RWSO1/1), (D) the pertussis component of DTP vaccine test 4 and reference pertussis vaccine (RWSO1/11) (E) the pertussis component of DTPvaccine test5 and reference pertussis vaccine (RWSO1/11).

Figure 2

Estimation of dose response regression lines of the pertussis component of DTP vaccine test and reference pertussis vaccine (RWSO1/11) by the parallel line method using WHO combistats software(dose response regression curves of the proportion of surviving mice transformed to a probit as a function of the dose): (A)The pertussis component of DTP vaccine test 1 and reference pertussis vaccine (RWSO1/11),(B) the pertussis component of DTP vaccine test 2 and reference pertussis vaccine (RWSO1/11),(C) the pertussis component of DTP vaccine test 3 and reference pertussis vaccine (RWSO1/1), (D) the pertussis component of DTP vaccine test 4 and reference pertussis vaccine (RWSO1/11) (E) the pertussis component of DTPvaccine test5 and reference pertussis vaccine (RWSO1/11).