Iannelli Mimmo, Martcheva Maia, Li Xue-Zhi
Dipartimento di Matematica, Universitá di Trento, 38050 Povo Trento, Italy.
Math Biosci. 2005 May;195(1):23-46. doi: 10.1016/j.mbs.2005.01.004. Epub 2005 Apr 26.
Several articles in the recent literature discuss the complexities of the impact of vaccination on competing subtypes of one micro-organism. Both with competing virus strains and competing serotypes of bacteria, it has been established that vaccination has the potential to switch the competitive advantage from one of the pathogen subtypes to the other resulting in pathogen replacement. The main mechanism behind this process of substitution is thought to be the differential effectiveness of the vaccine with respect to the two competing micro-organisms. In this article, we show that, if the disease dynamics is regulated by super-infection, strain substitution may indeed occur even with perfect vaccination. In fact we discuss a two-strain epidemic model in which the first strain can infect individuals already infected by the second and, as far as vaccination is concerned, we consider a best-case scenario in which the vaccine provides perfect protection against both strains. We find out that if the reproduction number of the first strain is smaller than the reproduction number of the second strain and the first strain dominates in the absence of vaccination then increasing vaccination levels promotes coexistence which allows the first strain to persist in the population even if its vaccine-dependent reproduction number is below one. Further increase of vaccination levels induces the domination of the second strain in the population. Thus the second strain replaces the first strain. Large enough vaccination levels lead to the eradication of the disease.
近期文献中的几篇文章讨论了疫苗接种对一种微生物竞争亚型影响的复杂性。无论是针对竞争性病毒株还是细菌的竞争性血清型，都已证实疫苗接种有可能将竞争优势从一种病原体亚型转移到另一种亚型，从而导致病原体替代。这种替代过程背后的主要机制被认为是疫苗对两种竞争性微生物的有效性差异。在本文中，我们表明，如果疾病动态受重复感染调节，即使疫苗接种完美，菌株替代也可能确实会发生。事实上，我们讨论了一个双菌株流行模型，其中第一种菌株可以感染已被第二种菌株感染的个体，并且就疫苗接种而言，我们考虑一种最佳情况，即疫苗对两种菌株都提供完美保护。我们发现，如果第一种菌株的繁殖数小于第二种菌株的繁殖数，并且在没有疫苗接种的情况下第一种菌株占主导地位，那么提高疫苗接种水平会促进共存，这使得第一种菌株即使其依赖疫苗的繁殖数低于1也能在种群中持续存在。疫苗接种水平的进一步提高会导致第二种菌株在种群中占主导地位。因此，第二种菌株取代了第一种菌株。足够高的疫苗接种水平会导致疾病根除。
