Vaccinations against diphtheria and tetanus are essential in providing immunity against these bacterial infections. The potency of diphtheria and tetanus toxoid vaccines can be measured using the in vivo toxin neutralization assay. The limit of potency of this assay was determined only for children. Therefore, we assessed the potency of adult vaccines using this assay to identify the feasibility of limit for adult vaccines.
Fifteen lots of tetanus-reduced diphtheria and tetanus-diphtheria-acellular pertussis vaccines were used. In vivo toxin neutralization and lethal challenge assays were conducted on each vaccine to calculate the potencies of the toxoids. National reference standards for toxins and antitoxins were used for in vivo toxin neutralization assay.
All 15 lots satisfied the limits of potency for lethal challenge assay. The potency of diphtheria and tetanus toxoids exceeded 1 and 8 units/mL, respectively, for in vivo toxin neutralization assay.
Although additional studies are required for new assays and limits, the current level of potency for adult vaccines as determined by in vivo toxin neutralization assay, was demonstrated in this study. Such efforts to improve assays are expected to promote the development of diphtheria and tetanus vaccines for adults and to contribute to vaccine self-sufficiency.
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To circumvent the limitations of the current golden standard method, colony-forming unit (CFU) assay, for viability of Bacille Calmette–Guérin (BCG) vaccines, we developed a new method to rapidly and accurately determine the potency of BCG vaccines.
Based on flow cytometry (FACS) and fluorescein diacetate (FDA) as the most appropriate fluorescent staining reagent, 17 lots of BCG vaccines for percutaneous administration and 5 lots of BCG vaccines for intradermal administration were analyzed in this study. The percentage of viable cells measured by flow cytometry along with the total number of organisms in BCG vaccines, as determined on a cell counter, was used to quantify the number of viable cells.
Pearson correlation coefficients of FACS and CFU assays for percutaneous and intradermal BCG vaccines were 0.6962 and 0.7428, respectively, indicating a high correlation. The coefficient of variation value of the FACS assay was less than 7%, which was 11 times lower than that of the CFU assay.
This study contributes to the evaluation of new potency test method for FACS-based determination of viable cells in BCG vaccines. Accordingly, quality control of BCG vaccines can be significantly improved.
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