Vaccine Types

A vaccine is a biological product developed by eliminating the disease-causing properties of microorganisms such as viruses and bacteria. It ensures that the person gains immunity and becomes protected against the disease agent by introducing the whole or a part of the microorganism, which no longer has the power to cause disease, to the body's defense mechanism. 

Studies for vaccine production in our country first began during the Ottoman Empire period. In a letter written to her country in 1721, Lady Mary Montagu, the wife of the British Ambassador, reported with amazement that "something called a vaccine" (variolation method) was being practiced against smallpox in Istanbul. This letter is one of the oldest available documents regarding vaccine production.

Following the development of the vaccine used in England in 1796 to protect against smallpox, different vaccine production methods were introduced to produce successful vaccines. Today, vaccine production methods are at a more advanced level, and reliable and sophisticated production methods are used to help protect the world from infectious diseases.

"The word 'vaccine' is derived from the 'Vaccinia virus,' which has a very low power to cause disease in humans and was used to protect against smallpox."

Depending on the agent that causes the targeted disease (called a pathogen; vaccines can generally be developed for diseases caused by bacteria or viruses), different vaccine production methods are used to create an effective vaccine. Just as there is more than one way to develop a vaccine, there can also be different forms of vaccine administration; the most well-known are injections with needles. However, there are also vaccines given orally in the form of drops. Additionally, in recent years, more innovative ways such as nasal sprays are being used and developed.

There are different vaccine production methods, each with its own unique benefits and examples.

Live Attenuated Vaccines

Live attenuated vaccines (also called attenuated vaccines) contain live viruses or bacteria whose ability to cause disease has been reduced or completely lost, but whose ability to replicate continues. Since live attenuated vaccines possess the ability to replicate, they are recognized very strongly by the body's immune system and generate a powerful immune response. They are advantageous in this respect.

Benefits: Since these types of vaccines contain a live pathogen, the immune system responds to them very well and usually remembers the pathogen for a very long time. Booster doses or reinforcement vaccines are not always needed.

Although their advantages are prominent, live vaccines are not recommended for individuals with weak immune systems and pregnant women, as they are live even though they cannot cause disease.

Examples: Measles, mumps, and rubella (MMR) vaccine, chickenpox (varicella) vaccine, polio vaccine (live oral drop vaccine)

Inactive Vaccines

While producing inactive vaccines, a live pathogen is taken and rendered ineffective, inanimate. Purification is performed with filters, and products that will increase the response and facilitate recognition by the immune system are added to turn it into a vaccine. When the vaccine is administered to the individual through injection, the inactivated pathogen is strong enough to generate an immune response, but since it is inanimate or fragmented, it cannot cause disease. In order to create immunity and provide full protection, a complete response can be obtained by presenting it to the immune system several times since it is inanimate or fragmented; therefore, multiple doses are usually required.

Benefits: Inactive vaccines can be produced in large quantities; they are safer because they are inanimate or fragmented.

Examples: Hepatitis A vaccine, polio vaccine (inactive), influenza vaccine, Covid-19 Vaccines (TURKOVAC, CoronaVac)

Subunit Vaccines

Subunit vaccines are inactive vaccines. They are made from only a part of the inanimate pathogen that can be recognized by the defense system, rather than the entire pathogen; therefore, they do not contain any live pathogens. Some important subunit vaccines are polysaccharide vaccines, conjugate vaccines, and protein-based vaccines.

• Polysaccharide vaccines are vaccines that contain a part recognizable by the immune system from the outer surface of pathogenic bacteria, which is covered with a type of sugar layer, in order to generate an immune response. These types of vaccines are not recommended for children under 2 years of age as they cannot generate a full response.
• Conjugate vaccines: The immune system cannot respond very well to pathogenic bacteria with a polysaccharide structure. They are produced by adding another protein or sugar structure to the parts of these bacteria that are not fully recognized by the immune system but have the potential to respond, thereby making them more easily recognizable by the immune system. Thus, a better response is obtained, and additionally, infants under 2 years of age can also respond and become protected.
• Protein-based vaccines are vaccines in which only a specific protein on the surface of a virus or bacterium is used in cases where that protein can be recognized and responded to by the immune system.
• Subunit vaccines can be made in one of two ways: by replicating the bacterium or virus and rendering it inanimate and obtaining only that unit, or as recombinant (by taking the coding information of the relevant structure and producing it in another easily reproducing living microorganism, which is usually a yeast, or in a laboratory environment).

Benefits: Subunit vaccines contain only a specific part of a pathogen, not the entire microorganism; therefore, they cannot cause disease or infection. This makes subunit vaccines suitable for people who should not receive "live" vaccines, such as young children, the elderly, and immunocompromised individuals.

Examples: Haemophilus influenzae type B (Hib) vaccine (conjugate), pneumococcal vaccine (polysaccharide or conjugate), hepatitis B (recombinant protein), acellular pertussis, MenACWY (conjugate).

Toxoid Vaccines

Some bacteria cause disease and even losses through the substances they secrete. These secretions, which generally harm humans, are called toxins. Some toxin-secreting bacteria have close relatives that do not have the ability to secrete toxins and are very common in the environment. Developing a vaccine directly against these types of bacteria may not always be possible since they are very common in the environment. In this case, ensuring that the immune system recognizes the toxins and produces antibodies that neutralize them against the toxins provides protection from the disease. Diphtheria and tetanus vaccines are such types of vaccines. Neutralizing the toxins they secrete with chemicals or heat, introducing them to the immune system, and ensuring that the immune system becomes responsive provides protection from the disease. However, they require regular booster doses.

"The purpose of toxoid vaccines is to provide humans with a way to neutralize these toxins with antibodies through vaccination."

Benefits: Toxoid vaccines are particularly effective in preventing diseases caused by certain agents that cause disease through their toxins, such as tetanus and diphtheria. Booster doses are generally recommended every 10 years.

Examples: Tetanus vaccine, diphtheria vaccine.

Viral Vector Vaccines

Viral vector vaccines are vaccines that use a harmless virus to carry the coding information of a subunit of a microorganism we want to introduce to the immune system to the individual's cells, in order to ensure the production of that subunit within the individual's cells.

Benefits: Viral vector vaccines generally generate a strong immune response. A booster dose may be needed to maintain immunity.

Examples: Ebola vaccine, COVID-19 vaccine (AstraZeneca and Johnson & Johnson)

Messenger RNA (mRNA) Vaccines

One of the newest fields in vaccine technology is the use of mRNA vaccines. It is based on the principle of delivering the coding information of a subunit of the microorganism we want to introduce to the immune system to the cells in the form of mRNA. When an mRNA vaccine is administered, the RNA material teaches our body how to produce a specific type of protein that is unique to the virus but does not make the person sick. The protein generates an immune response that includes the production of antibodies that recognize the protein.

Benefits: A very powerful technique for being able to create many vaccines rapidly. Potentially, the mRNA in the formulation can be changed to target a new antigen, and a large amount of vaccine material can be produced relatively quickly.

Examples: Pfizer-BioNTech COVID-19 vaccine

"Vaccines ensure that our bodies recognize microorganisms that can cause disease without becoming sick.

Vaccines teach our immune system to be protected from diseases without taking risks.

The main purpose of being vaccinated is to protect ourselves and the society from diseases."