Recently, the Comprehensive Group of the Joint Prevention and Control Mechanism of the State Council issued a plan to deploy the second dose of enhanced immunization. Who should get the "fourth shot" of vaccine? What is the "fourth shot" of vaccine? Focusing on social hot spot concerns, relevant experts of the joint prevention and control mechanism of the State Council gave answers. 1. Question: Who should receive the second dose of intensive vaccination? A: At this stage, the elderly and other high-risk groups continue to face the risk of infection. Vaccination is an important measure and means of epidemic prevention and control. In order to better protect the health and life safety of the people, according to the approval of vaccine research and development and emergency use, the high-risk population, the elderly over 60 years old, the population with more serious basic diseases and the population with low immunity can receive the second dose of booster immunization 6 months after the completion of the first dose of booster immunization. 2. Q: What's the use of intensive immunization now? A: The protective effects of COVID-19 vaccine mainly include antibody production, cellular immunity, immune memory, etc. After vaccination, antibody levels will decline over time. In addition, as the virus mutates, immune escape is also enhanced, making the role of antibodies weakened. However, the role of cellular immunity in preventing severe diseases and death is relatively lasting. Research shows that inoculation of booster needle can arouse the immune memory cells of the body, and also improve the antibody level, further consolidating the preventive effect on severe diseases and death. As long as the vaccination conditions are met, those who have not completed the booster immunization should complete the booster immunization as soon as possible according to the provisions of the immunization procedure, so as to have a better protective effect. 3. Question: Which vaccines can be inoculated in the second dose of intensive vaccination? A: At present, all 13 vaccines approved for conditional marketing or emergency use can be used for the second dose of booster immunization. Priority is given to the recommendation of sequential booster immunization, or the use of vaccines containing or having good cross immunity to Omicron virus strains. Sequential enhanced immunization refers to heterogeneous enhanced immunization with vaccines of different technical routes. If three doses of inactivated vaccine have been inoculated in the early stage, one of the recombinant protein vaccine, adenovirus vector vaccine or influenza virus vector vaccine can be selected during the second dose of booster immunization, which is also the vaccination combination recommended by the state. 4. Q: How safe is vaccination? A: The China Center for Disease Control and Prevention has monitored the adverse reactions of more than 3.4 billion doses and more than 1.3 billion people who have been vaccinated in China, and found that the incidence of adverse reactions of COVID-19 vaccines in China is comparable to other vaccines that are vaccinated throughout the year, and the incidence of adverse reactions of elderly people is slightly lower than that of young people. For the elderly, the Work Plan for Strengthening COVID-19 Vaccination for the Elderly has identified four vaccination taboos. If chronic diseases such as diabetes and hypertension are in a stable period, COVID-19 vaccine can be inoculated. 5. Question: Can the second dose of intensive vaccination be carried out after "positive" treatment? A: According to the current technical guidelines for COVID-19 vaccination, if COVID-19 infection is confirmed, the time interval between infection and COVID-19 vaccination should be more than 6 months. At present, the immune protection produced by simple infection is inferior to infection