BACKGROUND In November 2011, Malawi introduced the 13-valent pneumococcal conjugate vaccine (PCV13) into the routine infant schedule. Four to 7 years after introduction (2015-2018), rolling prospective nasopharyngeal carriage surveys were performed in the city of Blantyre. Carriage of Streptococcus pneumoniae vaccine serotypes (VT) remained higher than reported in high-income countries, and impact was asymmetric across age groups. METHODS A dynamic transmission model was fit to survey data using a Bayesian Markov-chain Monte Carlo approach, to obtain insights into the determinants of post-PCV13 age-specific VT carriage. RESULTS Accumulation of naturally acquired immunity with age and age-specific transmission potential were both key to reproducing the observed data. VT carriage reduction peaked sequentially over time, earlier in younger and later in older age groups. Estimated vaccine efficacy (protection against carriage) was 66.87% (95% CI 50.49-82.26%), similar to previous estimates. Ten-year projected vaccine impact (VT carriage reduction) among 0-9 years old was lower than observed in other settings, at 76.23% (CI 95% 68.02-81.96%), with sensitivity analyses demonstrating this to be mainly driven by a high local force of infection. CONCLUSIONS There are both vaccine-related and host-related determinants of post-PCV13 pneumococcal VT transmission in Blantyre with vaccine impact determined by an age-specific, local force of infection. These findings are likely to be generalisable to other Sub-Saharan African countries in which PCV impact on carriage (and therefore herd protection) has been lower than desired, and have implications for the interpretation of post-PCV carriage studies and future vaccination programs.

中文翻译：

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马拉维布兰太尔PCV13肺炎球菌疫苗接种后残留量高的决定因素：一项模型研究。

背景技术2011年11月，马拉维将13价肺炎球菌结合疫苗（PCV13）纳入了常规婴儿接种方案。引入后四到七年（2015-2018年），在布兰太尔市进行了滚动式鼻咽马车前瞻性调查。肺炎链球菌疫苗血清型（VT）的携带率仍高于高收入国家的报告，其影响在各个年龄段之间是不对称的。方法采用贝叶斯马尔可夫链蒙特卡洛方法拟合动态传输模型以调查数据，以深入了解PCV13后特定年龄VT运送的决定因素。结果随着年龄的增长和特定年龄的传播潜力，自然获得的免疫力的积累都是再现观察到的数据的关键。随着时间的流逝，VT滑车减少量达到峰值，在较年轻的年龄组中较早，在较晚的年龄组中较晚。估计的疫苗功效（防止运输）为66.87％（95％CI 50.49-82.26％），与之前的估计相似。在0-9岁之间的十年预测疫苗影响（降低VT运送）比在其他环境中观察到的要低，为76.23％（CI 95％68.02-81.96％），敏感性分析表明，这主要是由较高的局部感染力。结论布兰太尔PCV13肺炎球菌VT传播同时存在疫苗相关和宿主相关的决定因素，疫苗的影响由特定年龄的局部感染力决定。这些发现很可能会推广到其他撒哈拉以南非洲国家，这些国家的PCV对运输的影响（因此对畜群的保护）低于预期，