Recently, the Notice on Printing and Distributing the Implementation Plan for the Second Dose of Enhanced Immunization of COVID-19 Vaccine released on the website of the National Health Commission stipulates that at this stage, the second dose of enhanced immunization can be carried out among high-risk people, elderly people over 60 years old, people with serious basic diseases and people with low immunity on the basis of the first dose of enhanced immunization. All vaccines approved for conditional marketing or emergency use can be used for the second dose of booster immunization, including multiple intramuscular COVID-19 vaccines and the recombinant COVID-19 vaccine (adenovirus vector type 5) for Concino inhalation. Also as the second dose of booster immunization, what is the difference between the prevention principle of inhaled COVID-19 vaccine and intramuscular COVID-19 vaccine? Hu Ran, deputy director of the Immunization Planning Institute of Jiangsu Center for Disease Control and Prevention, said that the intramuscular COVID-19 vaccine is to stimulate the human body to produce T cells and form cellular immunity after injecting antigens into the human body; At the same time, it stimulates B cells to produce humoral immunity and IgG antibody. The antibody "patrols" the whole body with the blood circulation. Once the virus invading the body is found, it will be immediately killed. "The inhaled COVID-19 vaccine enters the human body through the respiratory mucosa. While producing cellular immunity and humoral immunity, it also produces secretory antibodies, such as secretory immunoglobulin (sIgA), in the mucosal system, especially in the respiratory mucosa. These antibodies combine with COVID-19 to form a complex, which prevents the virus from adhering to epithelial cells." Hu Ran explained that, as the cilia of the respiratory mucosa oscillate, These complexes are expelled from the body and the virus is eliminated. At the same time, the complex formed by the combination of sIgA and COVID-19 can also stimulate the mucous membrane to secrete a large amount of mucus, "flush" the mucosal epithelial cells, and prevent the virus from adhering again. SIgA can also enhance polypeptides with antibacterial or bactericidal activity in mucous membrane secretion, inhibit virus replication or kill virus, and can also generate resident memory B cells and T cells in respiratory mucosa, reducing virus replication. "One of the core technologies of the inhaled COVID-19 vaccine is to atomize the vaccine into particles with a diameter of 3-5 microns through the palladium vibrating screen on the atomizing device. Particles of this size can effectively enter our respiratory tract and go deep into the lungs. They can directly express antigens in the human body through cells and stimulate the mucous membrane to directly stimulate human immunity," Hu Ran told Science and Technology Daily. "As a vaccine approved for emergency use, the inhaled COVID-19 vaccine has relatively complete safety data." Hu Ran said that up to now, the inhaled COVID-19 vaccine has carried out a number of clinical studies at home and abroad, and the research results related to safety data have been reviewed and certified by experts at home and abroad. However, due to individual differences, some people will also have adverse reactions. Hu Ran introduced that the common adverse reactions of vaccination were dry mouth and oropharyngeal discomfort, headache and fever were occasionally seen, but the proportion was very low, which could be alleviated by drinking water and rest. After 2-3 days, the symptoms will disappear by themselves. "In general, studies carried out in adults who have received two or three doses of intramuscular inactivated vaccine show that the safety performance of the inhaled COVID-19 vaccine is excellent, the overall incidence of adverse reactions is low, and most of the reactions are mild. Within six months after intensive vaccination