季节性流感（简称"流感"）对我国儿童健康危害严重。接种疫苗是最有效的预防手段，但流感疫苗尚未纳入我国免疫规划，需公众自费接种，目前接种率仅2%。我国流感传播动力学机制，及儿童接种疫苗在人群层面的直接和间接保护效果尚缺乏系统、深入的研究，成为制定免疫策略的核心瓶颈之一。本研究通过构建“易感-暴露-感染-康复”传播动力学模型，结合基于马尔科夫链蒙特卡洛算法的贝叶斯方法，开展我国流感传播动力学机制研究；在此基础上，针对已为儿童提供免费接种的典型地区，定量测算疫苗接种在人群层面的直接和间接效果；进一步估计逐步将儿童免费接种推广到其他有条件地区以及全国的直接和间接效果。本研究将回答我国流感传播动力学关键参数，儿童接种流感疫苗对自身及其他人群的流感疾病负担的影响等关键科学问题。研究结果可为国家/地方政府制定儿童流感疫苗免疫策略提供直接科学证据。

Seasonal influenza (hereinafter refer to influenza) is associated with a substantial disease burden among children in China. Vaccination is the most effective method for prevention, but influenza vaccine is not covered by National Immunization Programme in China and the cost of vaccination is completely borne by the vaccinees. Currently, the uptake rate is only 2%. No systematic studies have addressed the questions with regards to transmission mechanism of influenza, and the direct and indirect effects of children vaccination programme at the population level in China, which could be one of the key bottlenecks for policy-making on vaccination. Using the Markov chain Monte Carlo method based on Bayesian theoretical framework, the proposed research is designed to clarify the transmission mechanism of influenza by developing Susceptible-Exposed-Infectious-Recovered transmission dynamic model. Then we will evaluate the direct and indirect effects of vaccination programme in children in these areas where free vaccination is available, and further explore the direct and indirect effects if such programme are gradually expanded to other areas and the whole country. This study aims to estimate the key epidemiological parameters of influenza, and quantify the impact of influenza vaccination programme in children on the disease burden of influenza among themselves and other age groups. It is believed that the deliverables of this research would provide scientific evidences for national and local policy-makers on influenza immunization strategy in children.