A screening study on the detection strain of Coxsackievirus A6: the key to evaluating neutralizing antibodies in vaccines

The increasing incidence of diseases caused by Coxsackievirus A6 (CV-A6) and the presence of various mutants in the population present significant public health challenges. Given the concurrent development of multiple vaccines in China, it is challenging to objectively and accurately evaluate the level of neutralizing antibody response to different vaccines. The choice of the detection strain is a crucial factor that influences the detection of neutralizing antibodies. In this study, the National Institutes for Food and Drug Control collected a prototype strain (Gdula), one subgenotype D1, as well as 13 CV-A6 candidate vaccine strains and candidate detection strains (subgenotype D3) from various institutions and manufacturers involved in research and development. We evaluated cross-neutralization activity using plasma from naturally infected adults (<i>n</i> = 30) and serum from rats immunized with the aforementioned CV-A6 strains. Although there were differences between the geometric mean titer (GMT) ranges of human plasma and murine sera, the overall trends were similar. A significant effect of each strain on the neutralizing antibody test (MAX/MIN 48.0 ∼16410.3) was observed. Among all strains, neutralization of the S112 strain by 15 different sera resulted in higher neutralizing antibody titers (GMT_S112= 132.0) and more consistent responses across different genotypic immune sera (MAX/MIN = 48.0). Therefore, S112 may serve as a detection strain for NtAb testing in various vaccines, minimizing bias and making it suitable for evaluating the immunogenicity of the CV-A6 vaccine.

柯萨奇病毒A6型（Coxsackievirus A6, CV-A6）引发疾病的发病率持续攀升，人群中同时存在多种突变毒株，这给公共卫生防控带来了严峻挑战。当前国内多款CV-A6疫苗同步处于研发阶段，客观精准评价不同疫苗的中和抗体应答水平颇具难度。而检测毒株的选择，是影响中和抗体检测结果的关键因素。

本研究由中国食品药品检定研究院（National Institutes for Food and Drug Control）收集了原型株Gdula、1株D1亚型毒株，以及来自多家研发机构与企业的13株CV-A6候选疫苗株与候选检测毒株（均为D3亚型）。

研究采用30名自然感染成人的血浆（n=30）与上述CV-A6毒株免疫大鼠的血清，开展交叉中和活性评价。尽管人血浆与小鼠血清的几何平均滴度（geometric mean titer, GMT）区间存在差异，但整体变化趋势一致。各毒株对中和抗体检测均存在显著影响，其最大值与最小值之比为48.0~16410.3。

在所有受试毒株中，15份不同血清对S112株的中和抗体滴度更高（GMT_S112=132.0），且针对不同基因型免疫血清的应答更为一致（MAX/MIN=48.0）。因此，S112株可作为适用于各类疫苗中和抗体检测的候选毒株，能够最大限度降低检测偏倚，适用于CV-A6疫苗的免疫原性评价。