Many people are not clear about the concept of “cold” and there are many misunderstandings. In fact, the concepts of “cold”, influenza (short for influenza) and upper respiratory tract infection (short for upper respiratory tract infection) are different, and the methods of prevention and treatment are not exactly the same. Although both colds and flu are caused by viral infections of the respiratory tract, they are two different diseases. Influenza, or influenza for short, is an acute respiratory infection caused by influenza viruses, with a high incidence and prone to fulminant epidemics or pandemics, with pathogens of three types of influenza viruses, A, B and C, spread mainly through airborne droplets. Clinically, there are acute high fever, malaise, generalized muscle pain, conjunctivitis and mild respiratory infection symptoms, although self-limiting, but the elderly and with chronic respiratory disease, heart disease is easy to complicate pneumonia. The main characteristic of influenza is epidemic, which can cause regional, national, or even worldwide pandemic, so epidemic is the main basis for clinicians to diagnose influenza. Since influenza viruses, especially type A viruses, are highly susceptible to mutation, the strains of influenza, or virus serotypes, tend to be different each year, with a general three-year epidemic peak, with a large number of cases and severe systemic symptoms that affect health and work capacity. In November this year, there was an epidemic of parainfluenza IV virus in Hong Kong, causing serious impact. The common cold, referred to as the flu, commonly known as “cold”, is the most common type of acute upper respiratory tract viral infections, although most occur in early winter, but any season, such as spring, summer can also occur, different seasons of the cold virus is not exactly the same. The main pathogens are rhinovirus, followed by parainfluenza virus, adenovirus, Egyptian virus, coxsackievirus and respiratory syncytial virus, which are often combined with bacterial infections. Early symptoms include dry and itchy throat, sneezing, nasal congestion and runny nose, which starts as clear watery nasal discharge and thickens after 2 to 3 days. Most common colds are sporadic and do not cause epidemics, but coronavirus infection can cause some epidemics. Colds are mostly self-limiting and usually heal after 5-7 days. The main preventive measures for influenza are: 1. Early detection of influenza patients, early isolation of patients in situ, and early treatment. During the epidemic period, large gatherings and group activities should be reduced; masks should be worn in public places, and less access to densely populated places. Open windows regularly every day to keep indoor air fresh. 2. Drug prevention: Amantadine hydrochloride is effective in preventing influenza A, but it is not effective for influenza B. Therefore, the type of the epidemic strain must be determined in the early stage of the epidemic before drug prevention can be carried out for the unprotected population. 3, vaccine prevention: the commonly used vaccines are attenuated vaccine and inactivated vaccine. The attenuated vaccine uses the nasal spray method, and the inactivated vaccine uses the subcutaneous injection method. Six months to one year after vaccination has the effect of preventing the same type of influenza. However, the strain of influenza virus often varies, so it is difficult to predict the type of virus prevalent in the current year, but only to speculate which type it may be, and the strain of vaccine manufacturing should be close to the prevalent strain.