With the weakening of the pathogenicity of Omicron virus, the popularization of vaccination and the accumulation of prevention and control experience, the epidemic prevention and control in China is facing new situations and tasks. On January 26, the National Health Commission announced that novel coronavirus infection would be adjusted from "Class B A" to "Class B B" on January 8, 2023. This is another major adjustment of the epidemic prevention and control policy since China began to implement strict Class A prevention and control measures for infectious diseases on January 20, 2020. The regulation policy of "Class B, Class A management" has been implemented for nearly 3 years. Why is it adjusted to "Class B, Class B management" this time? What is the main basis for policy adjustment? Does the adjustment mean that the prevention and control efforts are reduced? What changes will be brought about after the adjustment? Liang Wannian, the specially invited authoritative expert of the joint prevention and control mechanism of the State Council and the leader of the expert group of the leading group of the National Health Commission on COVID-19 epidemic response and disposal, responded to public concerns at the first time. Q: What is the main basis for the adjustment of COVID-19 infection from "Class B A" to "Class B B"? A: Classified management has always been a strategy for the prevention and control of infectious diseases in China. Dynamic adjustment has always been implemented. Scientific management according to law has always been the basic principle for China to deal with infectious diseases. At present, there are 40 kinds of legal infectious diseases in China, including 2 kinds of Class A, 27 kinds of Class B and 11 kinds of Class C. Class A infectious diseases include pestis and cholera. Class B infectious diseases include novel coronavirus pneumonia, SARS, AIDS, etc. Among them, the prevention and control measures of Class A infectious diseases shall be taken for novel coronavirus pneumonia, infectious atypical pneumonia and pulmonary anthrax in anthrax. Class C infectious diseases refer to those monitored and managed, including influenza, etc. Relevant conditions shall be met to adjust infectious diseases from "Class B, Class A" to "Class B, Class B". Under the premise of the law, according to the understanding of the nature and harmfulness of pathogens and diseases, according to the immunity of the population and the resistance of the health system, according to the current situation and future trend of the epidemic, the decision can be made by gathering the wisdom of experts, drawing on domestic and foreign experience, and comprehensively considering various factors. From the legal basis, when an infectious disease may cause serious harm to the human health and life safety of citizens, and may cause significant economic losses and social impact, the state can take intensive intervention measures against citizens and society. However, when the harm of infectious diseases to human health and life safety is weakened, and the impact on economy and society is reduced, the state should dynamically adjust the intensity of intervention measures to ensure that the prevention and control measures of infectious diseases are optimized and adjusted according to time and situation. When new infectious diseases appear, due to the lack of understanding of their etiology and epidemiological characteristics, their infectivity, pathogenicity and pathogenic variation characteristics are still unclear. In order to maximize the protection of people's life safety and health, since China responded to new infectious diseases such as SARS in 2003, highly pathogenic avian influenza in 2005, and influenza A (H1N1) in 2009, The effective experience is to include them in Class B infectious diseases at the first time, but implement control measures for Class A infectious diseases. However, with the continuous deepening of research and understanding of the epidemic law of diseases and pathogens, the accumulation of clinical treatment methods, research and application of vaccines and drugs, and effective prevention and control measures, SARS was once treated as "Class B A"