Is your understanding of ＂mixing＂ COVID-19 vaccine correct？

　　Recently, China began to deploy COVID-19 vaccine to strengthen immunization in sequence. So, is sequential vaccination "mixing" different brands of vaccines? In fact, sequential vaccination emphasizes vaccination with different technical routes at intervals. Then why sequential vaccination? Is there a similar deployment abroad?

　　Why sequential inoculation?

　　Sequential inoculation refers to interval inoculation (alternate inoculation) of vaccines with different technical routes. According to Shao Yiming, a member of the expert group of the vaccine research and development special class of the joint prevention and control mechanism in the State Council, China, at the press conference of the joint prevention and control mechanism on the 19th, sequential immunization is often used for viruses with strong variability and difficult to deal with.

　　Wang Huaqing, chief expert of immunization program of China CDC, said that some countries in America, Europe and Southeast Asia have started to implement sequential immunization.

　　The European Medicines Agency and the European Center for Disease Control and Prevention issued a statement in December, 2021, saying that many studies showed that mixed inoculation ("mixed inoculation") of adenovirus vector vaccine and mRNA (messenger RNA) vaccine could "produce a better antibody level" and "produce a better T-cell immune response than vaccines using the same technology". T cells are one of the defenses against diseases in human body.

　　The statement said that "mixed vaccination" can "provide richer vaccination options, especially when a vaccine cannot be vaccinated for some reason, which can reduce the impact on vaccine promotion".

　　Shao Yiming said that there are two main purposes to adopt sequential immunization: one is that different vaccines can complement each other, and the other is that different personal constitutions may have more side effects on a certain type of vaccine, and vaccination with different technical routes can avoid side effects.

　　Temporary guide to "mixed fighting"

　　Based on the existing research data, the World Health Organization issued the interim guidelines for "mixed vaccination" in COVID-19 in December 2021. This guide is based on the recommendations made by the WHO Strategic Advisory Expert Group and is applicable to all COVID-19 vaccines on the WHO emergency use list. The guidelines suggest that if the first dose is a viral vector vaccine, whether the second dose or the booster dose can be vaccinated with mRNA vaccine; or vice versa, Dallas to the auditorium If inactivated vaccine is inoculated at first, viral vector vaccine or mRNA vaccine can be inoculated later.

　　Up to now, the vaccines that have entered the WHO emergency list include: AstraZeneca vaccine in Britain, Johnson & Johnson vaccine, Mardner vaccine and Pfizer vaccine in the United States, Sinopharm vaccine and Kexing vaccine in China, Covaxin vaccine and Covovax vaccine in India, and Novavax vaccine in the United States. Among them, Kexing, Sinopharm and Covaxin are inactivated vaccines, Johnson & Johnson and AstraZeneca are adenovirus vector vaccines, Mardner and Pfizer are mRNA vaccines, and Novavax vaccine and CoVAX are recombinant protein vaccines.

　　According to the provisional guidelines, the existing research mainly involves the influence of "mixed beating" on human immunity. It is still the current standard practice to choose the same vaccine as the first shot when inoculating the second and third shots, but with the deepening of research, WHO will re-evaluate the advantages and risks of "mixed shots". With the release of more research data, it is not excluded to adjust the "mixed play" guide.

　　Many countries approve "mixed fighting"

　　On October 20, 2021, the US Food and Drug Administration revised the authorization for emergency use of vaccines in COVID-19, allowing vaccinators to choose vaccine booster needles with different brands than those previously vaccinated. Peter Marks, director of the Center for Biological Products Evaluation and Research of the US Drug Administration, said that the decision to allow "mixed injections" to strengthen needles aims to meet the needs of the people as much as possible.

　　After studying the test results of Spanish and British mixed vaccination with COVID-19 vaccine, the Canadian National Advisory Committee on Immunization announced new regulations in June 2021, allowing mixed vaccination with COVID-19 vaccine, so as to further accelerate the vaccination progress. The first dose of AstraZeneca vaccine, the second dose can choose the same vaccine, Pfizer or Mardner vaccine.

　　South Korea, Britain and other countries have started clinical trials on sequential vaccination of COVID-19 vaccine. In May 2021, the disease control department of Korea started the clinical trial of sequential vaccination. The first batch of subjects were about 500 people who had been vaccinated with one dose of AstraZeneca vaccine, and the second dose was vaccinated with other COVID-19 vaccines such as Pfizer. The results showed that people who were inoculated with AstraZeneca and Pfizer vaccine in sequence would increase the neutralizing antibody level by 6 times compared with those who were vaccinated with two doses of AstraZeneca vaccine.

　　In February, 2021, Oxford University in the United Kingdom launched a clinical trial of sequential vaccination of COVID-19 vaccine. AstraZeneca vaccine and Pfizer vaccine were mixed in the first phase clinical trial, and Mardner vaccine and Novavax vaccine were used in the second phase trial in April.

　　The results showed that the antibody level of volunteers who were vaccinated with Pfizer vaccine and then AstraZeneca vaccine was about 5 times higher than that of volunteers who were vaccinated with two doses of AstraZeneca vaccine, and the antibody level of volunteers who were vaccinated with AstraZeneca vaccine and then vaccinated with Pfizer vaccine was 9 times higher than that of those who were vaccinated with two doses of AstraZeneca vaccine. Vaccination with AstraZeneca vaccine first and then with Mardner or Novavax vaccine will produce higher antibody level than two doses of AstraZeneca vaccine.

　　According to Xinhua News Agency