Medical Biotechnology | A vaccine that only requires one shot - adenovirus vector vaccine for COVID-19

The recombinant COVID-19 vaccine (adenovirus vector) developed by a team led by Chen Wei, an academician of the Chinese Academy of Engineering and a researcher at the Academy of Military Medical Sciences of the Academy of Military Sciences, was conditionally approved for marketing registration by the National Medical Products Administration on February 25. This is the first adenovirus vector vaccine approved for the prevention of COVID-19 in my country, and it is another COVID-19 vaccine after the inactivated vaccine was put on the market, adding another weapon to the prevention of COVID-19 in my country and the world.

The new coronavirus vaccine started Phase I clinical trials in Wuhan on March 16, 2020, entered Phase II clinical trials in Wuhan on April 12, and started Phase III clinical trials in Pakistan on September 22. Before its approval, multi-center Phase III clinical studies had been conducted in more than 70 clinical research centers in five countries, and a total of nearly 50,000 subjects had been vaccinated.

The vaccine uses a single-shot immunization procedure, can be stably stored at 2-8°C, is easy to transport and store, and is intended for people over 18 years old. The vaccine has been authorized for emergency use in Pakistan and Mexico. According to multiple data analysis, in Pakistan's Phase III clinical trials, 28 days after a single shot of the vaccine, the protective efficacy of severe COVID-19 cases reached 100%, and the overall protective efficacy was 74.8%. It can be said that it is a high-quality vaccine that meets and exceeds the requirements of the World Health Organization in all technical standards, and has achieved a better unity of safety, effectiveness and accessibility.

So, what is the benefit of this new coronavirus vaccine that only requires one shot?

Mature technology and high safety

Equivalent to efficient combat by land, sea and air

The adenovirus vector COVID-19 vaccine constructs the gene of the COVID-19 S protein into the adenovirus genome. The recombinant adenovirus shell is still the shell protein of the adenovirus, but the gene inside contains the gene encoding the COVID-19 S protein. Therefore, after the adenovirus infects the host cell, the recombinant adenovirus and the COVID-19 S protein gene it carries enter the host cell, synthesize the S protein in the cytoplasm, and the S protein stimulates a series of immune responses.

The COVID-19 vaccine developed by Academician Chen Wei's team uses Ad5 adenovirus as a vector. Ad5 adenovirus is a non-enveloped double-stranded DNA virus with a strong ability to infect human cells. It is a virus that artificially cuts out the key gene fragment responsible for the replication of the virus, and cannot replicate but retains its ability to infect human cells. Therefore, it is called a replication-deficient adenovirus vector, which has a high safety. Ad5 adenovirus vector is a relatively mature platform and has been used in the development and production of Ebola vaccines.

In addition to mature technology and high safety, another feature of it is that it can stimulate cellular immunity while inducing humoral immunity. That is, it can induce humoral immunity to produce antibodies, bind to viruses, and prevent the viruses from entering human cells. They are recognized, engulfed, and degraded by macrophages outside the cells. For viruses that have already entered the cells by chance, cellular immunity can be activated to identify and secrete cytokines by killer T cells to lyse the infected cells.

If the immune response process is likened to a war between the immune system and foreign enemies, then the immune response induced by the adenovirus vector COVID-19 vaccine is equivalent to a joint sea, land and air operation, which can completely eliminate the enemy and naturally has better immunogenicity. It is worth mentioning that not all COVID-19 vaccines developed based on different technical routes can stimulate cellular immunity.

Single-dose vaccination has a high protection rate

No serious adverse reactions

Academician Chen Wei gave a detailed account of the characteristics of the approved adenovirus vector COVID-19 vaccine in an interview with CCTV on February 26:

This vaccine is the only one that can be administered with a single injection in my country. So far, two major types of vaccines have been developed in China, one is an inactivated vaccine and the other is an adenovirus vector vaccine. The safety and effectiveness of each vaccine are supported by certain data. But if you want to get fewer shots, or produce an immune response faster - with a protection rate of more than 60% in 14 days, or if you have to go abroad or perform a mission after getting one shot, the adenovirus vector COVID-19 vaccine is the first choice.

The protection rate for severe cases can reach over 90%. Compared with reducing infection, the role of vaccines in blocking severe cases is more worthy of attention. If a vaccine can reduce the incidence of severe cases, it can reduce the mortality rate. The vaccine has been clinically studied in Pakistan with more than 18,000 people, with a protection rate of 100% for severe cases and an overall protective efficacy of 74.8%. In a larger global clinical study, the protection rate for severe cases reached over 90%, which is particularly encouraging data.

There were no serious adverse reactions in the vaccinated population. So far, no serious adverse reactions related to the vaccine have been found among the people who have been vaccinated, especially in the Phase III clinical trial of more than 40,000 people.

The protection period of a single shot is at least 6 months. So far, the vaccine has a 6-month protection period data support, indicating that after one shot, there is no need for vaccination within 6 months. If the epidemic is not over after 6 months, you can also boost it with another shot, and the immune response can increase by 10 times or 20 times. According to the data, it is speculated that after two shots, the immune persistence can reach two years.

Vaccines are not perfect

Rational understanding and continued research

No vaccine is perfect. Although adenovirus vector vaccines have advantages that other vaccines do not have, and have been proven to be safe, effective, and accessible after Phase III clinical trials involving more than 40,000 people in multiple countries, some situations still need further observation and sufficient attention.

1. Since most people have been infected with adenovirus type 5, which serves as a vector, during their growth, they may have antibodies in their bodies that can neutralize the adenovirus vector. This "pre-existing immunity" may reduce the effectiveness of the vaccine.

2. The adenovirus genome is not integrated into the host genome, which may cause the recombinant adenovirus exogenous genes to be phagocytosed and cleared by the body's endothelial cells, thereby failing to continuously express the SARS-CoV-2 S protein, which is the active ingredient of the vaccine.

3. Due to the wide range of adenovirus infection and lack of targeting, adenovirus vectors may cause infection of other normal tissue cells while infecting target organs and target cells, thereby causing adverse reactions.

4. The operation and production of adenovirus vector vaccines must meet strict requirements, and the risks of viral vectors must be fully studied.

5. As a conditionally approved vaccine, the drug license holder should continue to carry out relevant research work in accordance with the requirements of the National Medical Products Administration, supplement and improve clinical trial data, gradually complete various additional conditions, and submit follow-up research results in a timely manner.

Although the COVID-19 epidemic has been effectively controlled, safe and effective vaccination is still the most powerful weapon to prevent the disease. Vaccination can stimulate the body to produce immunity against the new coronavirus and prevent infection with the new coronavirus. Therefore, it is recommended that all people aged 18 and above and under 59 should be vaccinated with the new coronavirus vaccine if there are no contraindications.

It should be noted that people aged 60 and above are the key population infected by the new coronavirus, and they should be vaccinated and protected. However, due to the relatively insufficient clinical trial data of the new crown vaccine phase III in my country for people over 60 years old, the National Medical Products Administration conditionally approved that it was not open to this age group. Recently, some provinces and cities have proposed solutions based on local actual conditions. For example: Beijing Center for Disease Control and Prevention issued a statement on its official WeChat account on March 2 that at present, Beijing has vaccinated some elderly people aged 60 and above who have vaccination needs and are in good physical condition in accordance with the overall arrangements of the country. In the next step, Beijing will carry out comprehensive vaccination of the elderly in a timely manner according to the opinions of the country. According to the progress of vaccine research and development and the results of subsequent clinical trials, the vaccination of people under 18 years old in the city will be arranged in accordance with the unified requirements of the state. I believe that it will not be long before my country can achieve new crown vaccination for all age groups.

Author: Yaohuluwa Medical Biotechnology Science Popularization Group