Colds can be broadly classified as common colds and influenza. Influenza is an acute respiratory infection caused by the influenza virus and is one of the major public health problems facing humanity. The epidemiology of influenza is characterized by sudden outbreaks, rapid spread, causing epidemics of varying degrees, seasonality, high incidence but low mortality rates (except for human avian influenza, generally only 0.003% to 0.03%). After droplets with influenza virus enter the respiratory tract, they bind to epithelial cells through specific receptors and enter the cells through endocytosis, replicating a large number of new daughter virus particles, which can spread through the respiratory mucosa and infect other cells, later causing overall influenza symptoms. Since influenza can infect the epithelial cells of the lower respiratory tract, it is not possible to classify influenza as epizootic. The relationship between influenza and episodic influenza can be represented in the following diagram. Based on viral nucleoproteins and matrix proteins, influenza viruses are classified into four types: A, B, C, and D (or A, B, C, and D). Influenza A is often epidemic-prone and can cause a worldwide influenza pandemic. Influenza B is often a local outbreak and does not cause a worldwide influenza pandemic. Influenza C mainly appears in a scattered form, mainly affects infants and children, and generally does not cause an epidemic. Type D is another influenza virus that has emerged in recent years. The H1N1 and H7N9 influenza viruses that we are familiar with are all influenza A viruses. Pathological changes are mainly manifested as clusters of ciliated epithelial cells in the respiratory tract, epithelial cell metaplasia, congestion and edema of mucosal cells in the lamina propria with mononuclear cell infiltration, etc. Pathological changes in cases of fatal severe influenza viral pneumonia are dominated by hemorrhage, severe tracheobronchitis and pneumonia, which are characterized by extensive necrosis of bronchial and fine bronchial cells, shedding of ciliated epithelial cells, fibrin exudation, inflammatory cell infiltration, hyaline membrane formation, congestion of alveolar and bronchial epithelial cells, interstitial edema, and mononuclear cell infiltration. Later changes include diffuse alveolar damage, lymphoid alveolitis, regeneration of septic epithelial cells, and even extensive tissue fibrosis. Severe cases may cause pneumonia due to secondary bacterial infections, mostly diffuse but also limited pneumonia. The difference between influenza and the common cold is as follows: Seasonal influenza is highly transmissible from person to person, and active prevention and control is more important than limited effective treatment measures: 1. Keep indoor air circulating, and avoid going to crowded places during the peak of the epidemic. 2. Use tissues when coughing and sneezing to avoid droplet transmission. 3, wash your hands often and thoroughly, avoid contact with mouth, eyes and nose with dirty hands. 4. Seek medical attention promptly if flu-like symptoms appear during the epidemic, reduce contact with others and try to rest at home. Influenza vaccination is the most effective means of preventing influenza and its complications that cannot be replaced by other methods. Priority groups for vaccination: infants and children aged 6-59 months; elderly people aged >60 years; adults and children with chronic respiratory diseases, cardiovascular diseases, kidney diseases, liver diseases, blood diseases and metabolic diseases; adults and children with immune suppression; people who are unable to take care of themselves and those who have difficulties in sputum evacuation due to neurological disorders and are at risk of aspiration of upper respiratory secretions; long-term residents of nursing homes and other chronic disease care institutions Women who plan to become pregnant during the flu season. Vaccination method and timing: Children aged 6 months to 9 years who have never received influenza vaccine or who have received only one dose in the previous year should receive two doses at an interval of 4 weeks, and then receive one dose each year before the influenza season, and one dose each year for other people; the vaccination route is intramuscular or deep subcutaneous injection, and it is recommended that infants and children receive intramuscular injection on the outer thighs; vaccination should start before October each year in most areas of China.