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How Do Vaccines Work?

Due to the widespread coronavirus disease 2019 (COVID-19), people have been waiting for a long time to get vaccinated. These days, with COVID-19 vaccines coming into our life, people are talking about vaccines every day. The Sungkyun Times (SKT) will now introduce the basic information of a vaccine and the detailed mechanism of the COVID-19 vaccine. In addition, the SKT will answer frequently asked questions (FAQ) about vaccines.

What is a Vaccine?

Immune System of Our Body and Its Response to Vaccines

Our body protects itself by using physical barriers such as the skin and cilia from a pathogenic bacterium: bacteria, viruses, parasites, and fungi. When a pathogen evades the physical barrier and gets into the body, our body’s immune system starts to work to attack them. There are two ways that the immune response can work: through innate immunity and through adaptive immunity. Innate immunity is a type of general protection that everyone is born with. When innate immunity works, our white blood cells fight with an invader. Adaptive immunity is an immunity system that develops throughout our lives by making antibodies to fight an invader. When a new germ enters our body for the first time, the innate system works alone to defend the germ and introduces a new antigen. After the fight, our body can have a new antibody as a memory cell that only reacts with that antigen. This antibody responds more quickly and more effectively than the first attack. Antibodies can also be gained from a mother during pregnancy. The conventional vaccine contains artificially weakened or inactive pathogens, and when put into our body, it creates a helpful environment for building antibodies. By getting vaccinated, our body can build new antibodies without getting sick and can generate antibodies rapidly when the disease enters.

Our Body’s Immune System (sharp.com)

History and Types of Vaccine

Even though human beings first learned about the fundamentals of the vaccine in B.C. 430 in Greece, utilizing the principle became possible by the 20th century. In the 18th century, smallpox, the most serious epidemic, was straining the whole of Europe. A British doctor, Edward Jenner, started a research after hearing that a woman appeared immune to smallpox after being afflicted by cowpox, an infectious disease to cows. Based on this, Jenner injected the pus of smallpox into a boy six weeks after the boy got cowpox, and the boy didn’t get smallpox. This made smallpox the first disease that human beings eradicated. However, the one who finally completed the modern vaccine that isolated and cultured antigen alone was Louis Pasteur, a French chemist and microbiologist in the 20th century. Typical types of modern vaccines are live-attenuated vaccines and inactivated vaccines. The difference between the two is the status of virus or bacteria. Live-attenuated vaccines use a weakened or attenuated germ, but inactivated vaccines use the killed version of the germ. Besides this, live-attenuated vaccines cost less, and immunity-lasting periods are longer than inactivated vaccines, but they have more side effects.

Exploring the Mechanisms of the COVID-19 Vaccines

Korea provides four kinds of COVID-19 vaccines made by four different manufacturers: AstraZeneca (AZ), Janssen, Pfizer, and Moderna. Since all of them have different mechanisms from conventional vaccines, they are neither live nor inactivated vaccines. AZ and Janssen are viral vector vaccines, and Pfizer and Moderna are mRNA vaccines. These two kinds of vaccines are derived from the idea of giving our body the blueprints of an antigen, not the actual antigen; viral vector vaccines inject the blueprint with a safe disease, and mRNA vaccines inject the blueprint only.

Vaccinated! (cdc.gov)

Viral Vector Vaccines

Viral vector vaccines have been studied since 1970. Viral vector vaccines serve a harmless “vector” to our body instead of a replicated virus, and the vector covers the antigen’s genetic code. So, it does not contain the actual antigen because the surface of the vaccine (the vector) and the outside of it (the genetic code) differs from the original antigen. In the case of the COVID-19 vaccine, when the vector enters our body’s cells, it uses our cell’s machinery to make a harmless version of the spike protein that lies on the surface of coronavirus. Spike proteins are a key factor when coronavirus infiltrates into our body. After our cells create the harmless spike protein, it appears on cell surfaces. This triggers our immune system to work and fight a virus. After the fight is over, the immune system gains the antibody to defeat the coronavirus. This mechanism is more stable in heat than the mRNA vaccines. However, it still needs a system to distribute in the condition that maintains the temperature of 4℃.

Viral Vector Vaccine (cdc.gov)

mRNA Vaccines

The viral vector vaccines are not classified as conventional vaccines because they do not inject the actual virus; still, they are not a completely new type because they deliver the antigen’s genetic code relying on the virus. However, a nucleic acid vaccine is a totally new approach; this vaccine directly teaches our cells how to make an antigen’s genetic code. Nucleic acid vaccines are studied for flu and rabies fields, but the COVID-19 vaccine is the first one to be commercialized. It has only been 25 years since the nucleic acid vaccines were studied. Nucleic acid is a substance in our body that regulates gene expression, and Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) are examples of this. DNA is the main body of our genes, and it holds all the information about which cell our body must create and which work each cell has to do. RNA interprets the information that DNA has and delivers the data to the protein-making part. Among various kinds of RNA, Messenger RNA (mRNA) only conducts passing, so mRNA can be explained as an order that contains the blueprint. The COVID-19 mRNA vaccine directly injects the mRNA itself that contains the direction to make a spike protein. After being vaccinated with an mRNA vaccine, our body produces a spike protein that works as an antigen, attacks it through our immune system, and generates an antibody. Since the mRNA mechanism creates an antigen inside of our body, it takes less time to manufacture the vaccines. However, RNA has a very unstable structure, so a temperature of -70℃ should be kept during the distribution process.

mRNA Vaccine (cdc.gov)

FAQ

The mechanisms used for developing COVID-19 vaccines are new to us. Also, since they don't have long-term verification, some people worry about getting vaccinated. Therefore, the SKT will answer the FAQ about vaccines.

Q1. Are COVID-19 vaccines safe even though they were developed rapidly?

Primarily, the reason why vaccines generally have a long development time, on average about ten years, is that vaccines do not possess big financial value to pharmaceutical companies. However, the COVID-19 pandemic made a huge demand, and there was tremendous support for developing vaccines. Also, there are originally three stages of clinical trials which take a long time, but those trials were done in parallel to be commercialized rapidly, and related institutions scaled down the approval steps. Even though the steps were reduced, they are still meaningful, and follow-up studies confirmed the vaccines' stability.

Q2. Does having side effects mean that the vaccine is effective?

After the shot, it is common to experience pain, redness, or swelling to the arm where you got the shot. Tiredness, headache, and muscle pains are also common. Since the vaccine triggers the immune system, those side effects can happen. However, side effects do not prove any effectiveness of the vaccine. According to a Seoul National University research team, there is no relationship between the side effects and the efficiency of the vaccine. Nevertheless, you should visit a doctor if you have serious side effects.

Q3. Are people perfectly free from COVID-19 after being vaccinated?

It is possible to come down with COVID-19 until two weeks after the 2nd shot because the formation of antibodies is insecure. Since the efficiency of the vaccine is not 100%, there is still the possibility of contracting the virus even after those two weeks have passed after the vaccination. However, when a vaccinated person comes down with COVID-19, the person is usually less vulnerable to serious illnesses. Still, it is important to be careful because vaccinated people can still spread COVID-19 to others, and there is still insufficient evidence about the vaccine's effectiveness to mutant viruses.

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