Modelling the effects of immunity on influenza transmission - implications for prevention and vaccine development

在疫情爆发之初，一个流感患者能感染多少人还不确定。一些数据表明，单代传播可感染10-20人。以这样的增长速度（即每3天10-20倍），流感爆发的传播几乎是不可阻挡的。其他数据表明，每个流感患者平均感染不到2人。在如此低的增长率下，控制将更加可行。我们的项目将使用历史上和当代流感爆发的数据，并建立数学模型，以以下方式解释流感爆发的增长速度：接触流感但未患病的人的比例（尽管如果进行仔细研究，可能有感染的证据）。这一比例约为33%。2. 通过免疫保护免受流感侵害的人口比例，无论是通过疫苗接种还是过去接触过自然流感感染（这一比例在多年未见流感的孤立人群中为0%，在几乎每个季节都接触过流感的城市化人群中为80%或90%）。3. 不同的人和群体之间的接触率不同——有些人可能经常接触，因此他们的免疫力会得到定期提高，而不会患上严重疾病；另一些人生活在较为孤立的环境中，可能很少接触到，但当他们接触到时，他们更有可能患上重病。4. 流感疫苗在诱导保护性免疫方面的作用——众所周知，如果疫苗与流行病毒很好地匹配，就会有很好的保护作用。5. 活病毒感染在诱导（短期）对更广泛的流感病毒的保护作用。我们的模型结果将用于指导疫苗设计和大流行规划。

There is uncertainty about how many people can be infected by a single person with influenza at the start of an outbreak. Some data suggest that a single generation of transmission can infect 10-20 other people. With such a rate of growth (ie 10-20 fold every 3 days) the spread of an influenza outbreak is virtually unstoppable. Other data suggest that each person with influenza infects less than 2 other people on average. With such a lower rate of growth, control would be more feasible. Our project will use data from historic and contemporary outbreaks of influenza and build mathematical models to explain the rate of growth of an influenza outbreak in terms of: 1. The proportion of people exposed to influenza who do not become ill (although there can be evidence of infection if careful studies are made). This proportion is about 33%. 2. The proportion of people who are protected from influenza by immunity, whether induced by vaccination or by past exposure to natural influenza infection (this can vary from 0% in isolated populations which have not seen influenza for many years up to 80 or 90% in urbanised populations that are exposed to influenza almost every season). 3. Different rates of contact between different people and groups of people - some may be exposed so often that their immunity is boosted regularly without them becoming severely ill; others, living in more isolated circumstances, may be rarely exposed, but when they are, they are more likely to become severely ill. 4. The effects of influenza vaccine in inducing protective immunity - it is well known that there is good protection if the vaccine is well matched to the circulating virus. 5. The effects of live virus infection in inducing (short-lived) protection against a wider range of influenza viruses. Our model results will be used to guide vaccine design and pandemic planning.