Are mRNA vaccines the hope of the future, and what role do they play?

In the early 2020s, neocoronavirus pneumonia broke out in China, causing people's work lives to come to a halt for a period of time; on Jan. 26, the Chinese Center for Disease Control and Prevention (CDC) isolated the neocoronavirus strain, which provided material for vaccine production and drug screening.

On January 16, local time, the U.S. announced the start of a clinical trial of a vaccine to prevent neocoronavirus pneumonia, and four people received the vaccine, which will be followed by a larger-scale experiment, more than a month earlier than previously expected, with the experimental vaccine being an mRNA vaccine.

On March 17, a Chinese company also announced that a vaccine jointly developed with the Institute of Bioengineering of the Academy of Military Sciences has also begun to enter the clinical stage and started recruiting volunteers; in addition, the mRNA vaccine developed in Shanghai, China, is expected to enter clinical trials in mid-April, and the vaccine is now producing specific antibodies in mice.

Currently the world's capable countries, are scrambling to develop a vaccine for the new coronavirus, and many experts have publicly stated that the elimination of the new coronavirus can not rely on herd immunity, the ultimate way to rely on the vaccine. So what happens in the human body after the vaccine is injected into it, and how is the virus eliminated?

The history of vaccines

Nowadays, newborn babies are vaccinated with the first vaccine of their lives within 1 to 2 days? BCG, then there was the Hepatitis B vaccine, DPT (a mixture of pertussis, diphtheria and tetanus) and so on, and it is because of these vaccines that human longevity has been greatly increased, and neonatal mortality has been dramatically reduced.

In ancient times, outbreaks of infectious diseases such as smallpox, bubonic plague, cholera, influenza, etc. killed thousands of people, with smallpox claiming the lives of more than half a billion, and causing at least 150 million deaths in 18th-century Europe alone.

Born in 1749, the British doctor Edward? Jenner, who knew many of the workers at the local milking plant, learned of a local saying that people infected with cowpox do not contract smallpox disease?

This claim caught Edward Jenner's attention. Jenner's attention, after much deliberation, in May 1796, Edward? Jenner injected a cowpox pus substance from a female laborer into an eight-year-old healthy boy, who quickly developed cowpox and then recovered, Edward? Jenner continued to inject smallpox into the boy, and as a result the boy did not develop smallpox.

This great discovery opened the way for mankind to defeat the virus scientifically, and Edward Jenner selflessly made the method available to the public. Jenner selflessly introduced the method to the world, and now Edward Jenner is also known as one of the greatest minds in immunology. Jenner is also known as the father of immunology.

Now we know that cowpox virus and smallpox virus have partly the same antigenic surface and can produce the same specific immunity, but the symptoms of cowpox are very mild and not fatal to most people; it was not until 1979 that the World Health Organization formally declared that the smallpox virus had been eliminated worldwide, and it is the only virus so far that has been eliminated by mankind completely.

Principle of vaccines

The principle of vaccines is closely related to the human immune system. Our body has developed a set of response mechanisms to deal with harmful foreign substances over a long period of time, starting with our skin, mucus, etc., which constitutes the body's first line of defense, blocking most foreign substances (including bacteria, viruses, and foreign objects, etc.) from entering the body.

However, the first line of defense also has leakage, such as skin damage, viruses directly into the lungs, etc., the next body's immune system will play a role, we can image the immune system as ? The police? The immune system can be viewed as a police officer, and the foreign substances as the bad guys. The bad guys? The whole thing is? The whole thing is the police catching the bad guys? The whole thing is a police action to catch the bad guys.

Foreign substances enter the human body, will soon be found by the body, and then sent phagocytes to phagocytosis of foreign substances, phagocytes are like the police patrolling the streets, whether they can meet the bad guys as well as whether they can recognize the bad guys depends on luck, so this line of defense is not everything.

If the destructive power of the virus is not strong, the immune system B cells in the recognition of pathogens (such as viruses), B cells will be converted to effector B cells, effector B cells will be based on the surface characteristics of the antigen to produce specific antibodies, specific antibodies to the antigen has a strong affinity for the antigen, can be a large number of adsorption in the antigen, so that the antigen loses the ability to infect, and then by the immune system to clear away.

Imaginatively speaking, antibodies are like a recognition system that can mark which are the bad guys and then be quickly removed by the patrol police, and the bad guy's appearance will be remembered by the immune system, and if this bad guy invades the human body again, the immune system will quickly release the antibodies, and the antibodies are specific, and they can only recognize and mark the specific antigens.

The principle of the vaccine is here, according to the response mechanism of the human immune system, we injected the inactivated or attenuated virus into the human body, we can let the immune system to produce an immune response, so as to memorize the information of the antigen, the inactivated or attenuated virus is the vaccine, the vaccine image is like a picture, tell the police what the bad guy looks like.

Viruses are made up of nucleic acids wrapped in protein shells. Inactivated viruses are those in which the nucleic acids have been destroyed but the protein shells can elicit an immune response from the human body; attenuated viruses need to be screened out, such as strains that can reproduce at 32 degrees Celsius inside the human nasal cavity but not at 37 degrees Celsius inside the body.

The difficulty of vaccine development

Simply put, it is to proliferate the virus in vitro, then inactivate the virus, and then inject the inactivated virus into the human body. It's very simple to say, but very difficult to do in practice.

Virus inactivation process to ensure that the destruction of viral nucleic acid at the same time, the surface antigen can not be destroyed; if the nucleic acid retains the activity of the human body may be infected, if the surface antigen is destroyed, the vaccine does not work, so the vaccine's clinical stage are very cautious, need to be experimented with in the animal body, and then the human body experiments, the entire research and development process generally need more than a year.

In addition, for RNA viruses, the mutation speed is very fast, the new coronavirus and influenza virus are RNA viruses, maybe when you develop the vaccine, the virus has mutated, and then the development of a new vaccine will have to start from the beginning, which is the reason why there are few vaccines for RNA viruses.

mRNA vaccine

In response to this new coronavirus, the United States was the first to announce that an mRNA vaccine was entering clinical trials, so what is an mRNA vaccine?

This has to start from the principle of viral proliferation in the human body, RNA viruses, for example, can be divided into positive-stranded RNA and negative-stranded RNA, positive-stranded RNA is similar to the human body mRNA, can be directly translated into proteins in the body's cells, while the negative-stranded RNA needs to use the RNA enzyme to synthesize their own templates for the opposite of the RNA, and then translated into proteins; this time, the new crown of the virus belongs to a single-stranded The new coronavirus is a single-stranded positive-stranded RNA virus.

The mRNA vaccine is from the perspective of the virus translation of protein, to the positive-stranded RNA virus, for example, we modify the virus RNA, only retain its ability to translate protein, and then made into an mRNA vaccine; mRNA vaccine can be translated in the body of the antigenic proteins, so as to cause the body's immune response, but only the protein does not have the ability to infect.

At the same time, mRNA will be broken down after being used in the human body, and will not be integrated into the human genome, so compared with traditional vaccines, mRNA vaccines are safer and have a better immune response, and in recent years, with the development of gene-transcription technology, the research and development cycle of mRNA has become shorter, and the research and development costs are lower.

But mRNA vaccines also have shortcomings, for example, mRNA is easily destroyed by RNA cleaving enzymes in the body, and the stability of mRNA is very poor, in addition, how to deliver the mRNA to the cells efficiently is also a difficult point.

In addition to DNA vaccines, DNA vaccines and RNA vaccines are collectively known as nucleic acid vaccines, and there are some ways to overcome the shortcomings of nucleic acid vaccines, and I believe that with the development of medical technology, nucleic acid vaccines are highly efficient and inexpensive, and will be the direction of future vaccine development.