Typhoid vaccines based on protein-conjugated capsular Vi polysaccharide (TCVs) prevent typhoid in infants and young children. Analysis of the serum anti-Vi IgG response following immunisation against typhoid confirms the immunogenicity of TCVs and forms an important part of the pathway to licensing. Comparative studies could expedite the licencing process, and the availability of a standardised ELISA method alongside the 1st International Standard (IS) 16/138 for anti-typhoid capsular Vi polysaccharide IgG (human) will facilitate this process. To this end, a non-commercial ELISA based on a coat of Vi and poly-l-lysine (Vi-PLL ELISA) was evaluated by 10 laboratories. Eight serum samples, including IS 16/138, were tested in the standardised Vi-PLL ELISA (n = 10), a commercial Vi ELISA (n = 3) and a biotinylated Vi ELISA (n = 1). Valid estimates of potencies relative to IS 16/138 were obtained for all samples in the Vi-PLL ELISA and the commercial ELISA, with good repeatability and reproducibility evident from the study results and concordant estimates obtained by the two ELISA methods. The study demonstrates that the Vi-PLL ELISA can be used in clinical trial studies to determine the immunogenicity of TCVs.

基于蛋白缀合荚膜Vi多糖（TCV）的伤寒疫苗可预防婴幼儿伤寒。针对伤寒免疫后对血清抗Vi IgG应答的分析证实了TCV的免疫原性，并构成了许可途径的重要组成部分。进行比较研究可以加快许可流程，并且针对第一类国际标准（IS）16/138的抗伤寒性荚膜Vi多糖IgG（人类），可以使用标准化的ELISA方法来促进这一过程。为此，由10个实验室评估了基于Vi和聚-1-赖氨酸涂层的非商业ELISA （Vi-PLL ELISA）。在标准的Vi-PLL ELISA（n  = 10），商业Vi ELISA（n = 10）中测试了八份血清样品，包括IS 16/138。n  = 3）和生物素化的Vi ELISA（n  = 1）。对于Vi-PLL ELISA和商业ELISA中的所有样品，均获得了相对于IS 16/138效力的有效估计，从研究结果和通过两种ELISA方法获得的一致估计中可以明显看出良好的可重复性和可重复性。该研究表明，Vi-PLL ELISA可用于临床试验研究中以确定TCV的免疫原性。