流感具有明显的季节性,几乎每年深秋、冬季和春季,都会有或大或小的流感暴发流行。流感流行北方重于南方,而且北方有明显的冬春季节性高峰。在温带和寒温带地区,流行通常发生在冬春季;而在热带和亚热带地区,则更多是在夏季流行。流感在世界各地均可发生。但各地之间的发病率有较大差异。这种地区分布的差异与病毒抗原的变异、人群密集程度、交往频度、传染 Influenza has obvious seasonal, almost every year late autumn, winter and spring, there will be large or small flu outbreak. Influenza pandemic north heavier in the south, and the north has obvious seasonal peak in winter and spring. In temperate and frigid regions, prevalence usually occurs in winter and spring; in tropical and subtropical regions, it is more prevalent in summer. Flu can happen anywhere in the world. However, there is a big difference in the incidence rates between different places. The differences in the distribution of this area are closely related to the variation of virus antigens, population density, frequency of contacts, infection