Relationship between immune response to pneumococcal conjugate vaccines in infants and indirect protection after vaccine implementation

<b>Introduction</b>: <i>Streptococcus pneumoniae</i> is a leading cause of morbidity and mortality worldwide. Widespread infant vaccination with pneumococcal conjugate vaccines (PCVs) substantially reduced vaccine-serotype pneumococcal disease by direct protection of immunized children and indirect protection of the community via decreased nasopharyngeal carriage and transmission. Essential to grasping the public health implications of pediatric PCV immunization is an understanding of how PCV formulations impact carriage. <b>Areas covered</b>: Using clinical evidence, this review examines how the immune response to PCVs is associated with subsequent nasopharyngeal carriage reduction in vaccinated infants and toddlers. By combining direct and indirect protection, carriage reduction results in a reduced spread of vaccine serotypes, and eventually, a decrease in vaccine serotype disease incidence in community members of all ages. <b>Expert opinion</b>: The current review presents some of the aspects that influence the overall impact of PCVs on vaccine-serotype carriage, and thus, spread. The link between reduction of vaccine-serotype carriage and the eventual reduction of vaccine-serotype disease in the wider community is described by comparing data from current PCVs, specifically with respect to their ability to reduce carriage of some cross-reacting serotypes (i.e. 6A versus 6B and 19A versus 19F).

**引言**：*肺炎链球菌（Streptococcus pneumoniae）*是全球范围内发病率与死亡率的主要致病诱因之一。通过肺炎球菌结合疫苗（pneumococcal conjugate vaccines, PCVs）开展的广泛婴儿疫苗接种，凭借对免疫儿童的直接保护，以及通过降低鼻咽定植与传播实现的社区间接保护，大幅降低了疫苗血清型肺炎球菌疾病的发生。明晰儿科肺炎球菌结合疫苗免疫的公共卫生意义，核心在于理解肺炎球菌结合疫苗的制剂如何影响细菌定植。

**综述范围**：本综述依托临床证据，探讨了肺炎球菌结合疫苗的免疫应答与接种疫苗的婴幼儿后续鼻咽定植减少之间的关联。通过结合直接与间接保护作用，定植减少可降低疫苗血清型菌株的传播，最终使全年龄段社区人群的疫苗血清型疾病发病率下降。

**专家观点**：本综述阐述了影响肺炎球菌结合疫苗对疫苗血清型定植乃至传播整体效果的若干要素。通过对比现有肺炎球菌结合疫苗的相关数据，尤其是其降低部分交叉反应血清型（即6A与6B、19A与19F）定植的能力，阐明了疫苗血清型定植减少与更广范围内疫苗血清型疾病最终减少之间的内在关联。