At present, many people infected with COVID-19 are gradually recovering. However, many people worry whether they will be infected again if COVID-19 strains are different. To this end, the reporter of Science and Technology Daily interviewed Zhang Boli, an academician of the CAE Member, and asked him to answer questions about the secondary infection of COVID-19. The probability of secondary infection within 3-6 months after turning negative is low. "The probability of re infection with COVID-19 is mainly related to the human immune level, virus strain variation and personal protection in the later stage." Zhang Boli said that compared with the early variant, Omikron may cause more breakthrough infections and repeated infections. However, Zhang Boli said that people should not worry too much. Although there is no evidence from a large sample of people to show the specific time of continuous immunity after the infection of the Omicron mutant virus strain, the human immune system has been playing a role after the infection of COVID-19. According to current clinical observation, the probability of secondary infection of COVID-19 within 3-6 months after infection is relatively low. At the same time, many people worry that secondary infection with COVID-19 will aggravate the symptoms. In this regard, Zhang Boli said that the symptoms of secondary infection with COVID-19 were related to many factors, such as whether there were underlying diseases, the dose of virus infection, and personal physical conditions. However, according to most reports at present, as the body has developed immunity, the symptoms of the second infection will generally be lighter than the last one. However, he stressed that there were also a few research reports that patients with reinfection had a higher risk of complications, including lung, cardiovascular, diabetes, gastrointestinal and nervous system complications, compared with patients who had only been infected once. It is recommended to vaccinate COVID-19 vaccine six months after recovery "Although it is unlikely to re infect the same COVID-19 variant in a short time, people with poor immunity are prone to repeated infection, including the elderly, infants, people with basic diseases and people with immune deficiency. There is a risk of secondary infection in the short term, especially when facing new variants." Zhang Boli introduced that people in high-risk positions such as doctors and nurses, The work environment is characterized by high risk of transmission, multiple exposure to mutant strains, high work intensity and high risk of secondary infection. "In order to avoid the re infection of COVID-19 mutant strain, we should continue to do a good job of personal protection after turning negative." Zhang Boli stressed that COVID-19 vaccine can be inoculated after 6 months of "Yangkang", and it is best to use sequential strategy to inject xenogeneic vaccine to strengthen the immune barrier. For those recovered from COVID-19 infection, the best way to prevent secondary infection is still to implement protective measures, including wearing masks, paying attention to hand hygiene, paying attention to rest, frequent ventilation, keeping social distance, etc. Especially for the elderly and children with "positive to negative", attention should be paid to keeping warm, gathering as little as possible, ensuring good health habits, paying attention to nutritious diet, enhancing immunity, and minimizing the risk of re infection. In case of re infection, we must first distinguish between "re positive" and secondary infection. "Reyang" occurs within 2-3 weeks after turning negative, and the patient generally has no obvious clinical symptoms, mainly due to the positive detection of residual virus fragments in the body, which is generally not infectious; The second infection usually occurs within a few months to a year after the first infection, which is equivalent to a new infection. Generally, there are clinical symptoms and virus nuclei