Health Protection Services Colindale, Health Protection Agency, London, United Kingdom.
PLoS One. 2012;7(7):e39927. doi: 10.1371/journal.pone.0039927. Epub 2012 Jul 13.
England and Wales recently replaced the 7-valent pneumococcal conjugate vaccine (PCV7) with its 13-valent equivalent (PCV13), partly based on projections from mathematical models of the long-term impact of such a switch compared to ceasing pneumococcal conjugate vaccination altogether.
A compartmental deterministic model was used to estimate parameters governing transmission of infection and competition between different groups of pneumococcal serotypes prior to the introduction of PCV13. The best-fitting parameters were used in an individual based model to describe pneumococcal transmission dynamics and effects of various options for the vaccination programme change in England and Wales. A number of scenarios were conducted using (i) different assumptions about the number of invasive pneumococcal disease cases adjusted for the increasing trend in disease incidence prior to PCV7 introduction in England and Wales, and (ii) a range of values representing serotype replacement induced by vaccination of the additional six serotypes in PCV13.
Most of the scenarios considered suggest that ceasing pneumococcal conjugate vaccine use would cause an increase in invasive pneumococcal disease incidence, while replacing PCV7 with PCV13 would cause an overall decrease. However, the size of this reduction largely depends on the level of competition induced by the additional serotypes in PCV13. The model estimates that over 20 years of PCV13 vaccination, around 5000-62000 IPD cases could be prevented compared to stopping pneumococcal conjugate vaccination altogether.
Despite inevitable uncertainty around serotype replacement effects following introduction of PCV13, the model suggests a reduction in overall invasive pneumococcal disease incidence in all cases. Our results provide useful evidence on the benefits of PCV13 to countries replacing or considering replacing PCV7 with PCV13, as well as data that can be used to evaluate the cost-effectiveness of such a switch.
英格兰和威尔士最近用 13 价肺炎球菌结合疫苗（PCV13）替代了 7 价肺炎球菌结合疫苗（PCV7），部分原因是基于数学模型对这种转变与完全停止肺炎球菌结合疫苗接种相比的长期影响的预测。
使用分区确定性模型来估计 PCV13 引入之前控制感染传播和不同肺炎球菌血清型组之间竞争的参数。使用最佳拟合参数在个体基础模型中描述英格兰和威尔士肺炎球菌传播动态和疫苗接种计划改变的各种选择的效果。使用（i）针对英格兰和威尔士 PCV7 引入前疾病发病率上升趋势调整的侵袭性肺炎球菌疾病病例数量的不同假设，以及（ii）代表疫苗接种引起的血清型替代的一系列值来进行多种方案。PCV13 中的另外六种血清型。
大多数考虑的方案表明，停止使用肺炎球菌结合疫苗将导致侵袭性肺炎球菌病发病率增加，而用 PCV13 替代 PCV7 将导致总体下降。然而，这种减少的规模在很大程度上取决于 PCV13 中额外血清型引起的竞争程度。该模型估计，在 PCV13 接种 20 多年后，与完全停止肺炎球菌结合疫苗接种相比，可预防约 5000-62000 例侵袭性肺炎球菌病病例。
尽管在引入 PCV13 后不可避免地存在血清型替代效应的不确定性，但该模型表明所有情况下总体侵袭性肺炎球菌病发病率都会降低。我们的研究结果为用 PCV13 替代或考虑用 PCV13 替代 PCV7 的国家提供了关于 PCV13 益处的有用证据，以及可用于评估这种转变的成本效益的数据。
