Dushoff Jonathan, Plotkin Joshua B, Viboud Cecile, Simonsen Lone, Miller Mark, Loeb Mark, Earn David J D
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey, United States of America.
PLoS Med. 2007 May;4(5):e174. doi: 10.1371/journal.pmed.0040174.
Epidemic influenza causes serious mortality and morbidity in temperate countries each winter. Research suggests that schoolchildren are critical in the spread of influenza virus, while the elderly and the very young are most vulnerable to the disease. Under these conditions, it is unclear how best to focus prevention efforts in order to protect the population. Here we investigate the question of how to protect a population against a disease when one group is particularly effective at spreading disease and another group is more vulnerable to the effects of the disease.
We developed a simple mathematical model of an epidemic that includes assortative mixing between groups of hosts. We evaluate the impact of different vaccine allocation strategies across a wide range of parameter values. With this model we demonstrate that the optimal vaccination strategy is extremely sensitive to the assortativity of population mixing, as well as to the reproductive number of the disease in each group. Small differences in parameter values can change the best vaccination strategy from one focused on the most vulnerable individuals to one focused on the most transmissive individuals.
Given the limited amount of information about relevant parameters, we suggest that changes in vaccination strategy, while potentially promising, should be approached with caution. In particular, we find that, while switching vaccine to more active groups may protect vulnerable groups in many cases, switching too much vaccine, or switching vaccine under slightly different conditions, may lead to large increases in disease in the vulnerable group. This outcome is more likely when vaccine limitation is stringent, when mixing is highly structured, or when transmission levels are high.
在温带国家，每年冬季流行性感冒都会导致严重的死亡率和发病率。研究表明，学童在流感病毒传播中起关键作用，而老年人和幼儿最易感染该疾病。在这种情况下，尚不清楚如何最有效地集中预防措施以保护人群。在此，我们研究当一组人群在传播疾病方面特别有效而另一组人群更易受疾病影响时，如何保护人群免受疾病侵害的问题。
我们建立了一个简单的流行病数学模型，该模型包括宿主群体之间的分类混合。我们在广泛的参数值范围内评估不同疫苗分配策略的影响。通过这个模型，我们证明最佳疫苗接种策略对人群混合的分类性以及每组疾病的繁殖数极为敏感。参数值的微小差异可能会使最佳疫苗接种策略从侧重于最易感染个体转变为侧重于最具传播性的个体。
鉴于有关相关参数的信息有限，我们建议疫苗接种策略的改变虽可能有前景，但应谨慎对待。特别是，我们发现，虽然在许多情况下将疫苗转向更具传播性的群体可能会保护易感染群体，但过度转移疫苗或在略有不同的条件下转移疫苗，可能会导致易感染群体中的疾病大幅增加。当疫苗供应受限、混合结构高度结构化或传播水平较高时，这种结果更有可能出现。
