Pharmaceutical Biotechnology | The “new way” to give booster shots—what exactly is sequential immunization?

At present, the number of newly confirmed local cases and asymptomatic infections is increasing rapidly across the country, community transmission in some areas has not been blocked, the COVID-19 epidemic is still running at a high level, and the prevention and control situation is severe and complicated, especially the epidemic situation in Shanghai and Jilin. The currently popular Omicron variant is highly contagious, spreads quickly and the transmission process is hidden, and vaccination with the new crown vaccine is the best measure to reduce severe illness and death.

On February 19, the press conference of the Joint Prevention and Control Mechanism of the State Council announced the launch of the sequential vaccination of the new crown vaccine in China. According to incomplete statistics from the news media, as of March 28, at least 19 provinces across the country have expressed their willingness to promote sequential vaccination, and a total of 12.191 million people have been vaccinated through sequential vaccination.

What is sequential immunization? Why do we need to do it? What are its advantages? Who is it suitable for?

"Joint operations" against the most cunning viruses Sequential immunization refers to the interval vaccination (alternation vaccination) of vaccines with different technical routes (heterologous vaccines), that is, under the premise of considering safety, the use of vaccines with different technical routes is carried out according to a certain vaccination time interval and vaccination dose. Sequential immunization is a way of booster vaccination. Booster immunization refers to the vaccination that is carried out after the completion of vaccination, according to the disappearance of antibodies, to maintain the body's continuous immunity to the virus. For example, at this stage, the new crown inactivated vaccine is administered in two injections, and another injection is administered according to the degree of decline in the body's antibody level.

Enhanced immunization includes two modes: homologous and heterologous vaccination. Sequential immunization belongs to heterologous vaccination, so some countries call it "mixed vaccination". It has the effect of stimulating and enhancing the body's immunity and effectively neutralizing various COVID-19 virus variants. According to previous experience in infectious disease prevention and control, a single vaccine can deal with conventional viruses, but for cunning and mutating viruses, different vaccines must be implemented to "combine operations".

The advantages of sequential immunization are: first, different vaccines can complement each other; second, it can reduce side effects for some people. Due to different physical conditions, some people may have more severe side effects to a certain vaccine, while others may have less severe side effects. By changing the vaccine, the occurrence of side effects can be reduced.

Studies have shown that sequential immunization has significant effects. The effects of sequential immunization have been supported by many clinical studies. In February 2021, the University of Oxford in the UK conducted a clinical trial of sequential vaccination of the new crown vaccine. The results of the test showed that volunteers who received the Pfizer vaccine first and then the AstraZeneca vaccine produced about 5 times the antibody level of volunteers who received two doses of the AstraZeneca vaccine; the antibody level produced by the AstraZeneca vaccine first and then the Pfizer vaccine was 9 times higher than that of the two doses of the AstraZeneca vaccine; the antibody level produced by the AstraZeneca vaccine first and then the Moderna or Novavax vaccine will be higher than that of the two doses of the AstraZeneca vaccine.

Recently, a booster immunization study jointly published by the Key Laboratory of Pathogenic Microbiology and Immunology of the Chinese Academy of Sciences, the Institute of Microbiology of the Chinese Academy of Sciences and other cooperative units showed that among the subjects who had completed two doses of inactivated vaccine for 4 to 8 months, the immune effect of CanSino's adenovirus vector COVID-19 vaccine was the strongest, and the level of neutralizing antibodies against the original strain was 7 times that of the sequential booster of the recombinant protein vaccine. In addition, the study also showed that booster immunization with adenovirus vector COVID-19 vaccine can provide the strongest protection against the Omicron mutant strain.

Sequential immunization is a process of continuous improvement of immunization strategies and a decision made based on scientific evidence. In fact, the sequential immunization strategy has long been used in my country. For example, the polio vaccine adopts a sequential immunization procedure. The first two doses are inactivated trivalent polio vaccine, and the last two doses are bivalent attenuated live vaccine. It has played a huge role in preventing and eliminating polio in my country.

Conditions and methods for implementing sequential immunization in my country At the press conference of the Joint Prevention and Control Mechanism of the State Council on February 19, relevant leaders of the National Health Commission stated that in order to better prevent and control the new crown pneumonia epidemic, the current immunization strategy will be supplemented and improved, and sequential immunization will be added to the original homologous booster immunization model. The specific plan is: For people who are 18 years old or older and have received 2 doses of inactivated vaccines for more than 6 months, when they receive the third booster shot, they can choose recombinant protein vaccines or adenovirus vector vaccines. Vaccination conditions:

The first is people over 18 years old;
The second is to complete 2 doses of domestically produced inactivated new coronavirus vaccine;

Third, complete the two-dose vaccination, and the interval between sequential booster vaccinations should not be shorter than 6 months;

Fourth, no booster immunization has been carried out, that is, the third shot has not been given.

Note:

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For the target population, either homologous booster vaccination or sequential booster vaccination can be selected. Both homologous booster vaccination and sequential booster vaccination should be implemented in people aged 18 years and over who have completed the full course of vaccination for more than 6 months.

Those who have received adenovirus vector COVID-19 vaccine or recombinant COVID-19 vaccine (CHO) do not need to undergo sequential immunization at this stage. That is, if the first shot is an adenovirus vector vaccine, the booster shot must also be given after at least 6 months. For those who have completed 3 doses of the full immunization with the COVID-19 recombinant protein vaccine, there is currently no need for booster immunization.

If a homologous booster vaccination has been carried out before the start of sequential vaccination, no further sequential vaccination is required according to current regulations.

Before vaccination, you must check whether you meet the four conditions for sequential vaccination. You must bring relevant certificates when you are vaccinated, take personal protection measures according to the requirements of epidemic prevention and control, and cooperate with the work of the vaccination site personnel. After vaccination, stay on site for 30 minutes as required. In short, a large number of clinical studies have proved that vaccination with the new crown vaccine is still the most effective, safest and most economical measure to prevent and control new crown pneumonia. For a special virus like the new coronavirus, strengthening immunity, especially sequential immunity, is of great significance for protecting susceptible populations and effectively curbing the spread of the epidemic.

Author: Yaohuluwa Medical and Biological Science Popularization Group