Vaccine – Introduction, Types & Working

Vaccine – Introduction, Types & Working


In the last article, we got to know about coronavirus. We discussed some of the basics of COVID-19 disease. Now in this article, we will be discussing vaccine production and many aspects associated with it.

Before we jump directly to vaccine production, it is important to know some basics of the immune system. Basically, the vaccine is a product of loopholes of the immune system which is benefiting humans. Our immune system is comprised of 2 parts. i.e. innate and adaptive immune system. They work together to protect us from the infection. Both have different roles and modes of action.

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Innate Immune System

The innate immune system is kind of nonspecific and the opposite is true for the adaptive immune system. The innate immune system consists of physical-chemical and biological barriers along with the whole system of immune cells.  It consists of neutrophils, macrophage, monocytes, and also some chemical factors like cytokines and complements.

Adaptive Immune System

The adaptive immune system included dendritic cells, T cells, B cells, and antibodies which are collectively known as immunoglobulin. Immunoglobulin interacts with antigens present on pathogens. This antigen-presentation, mounting response, and role of the memory cell is the core of the adaptive immune system. The adaptive immune response is catered against a specific antigen.

(Image Credits: Saswati Panda and Jake L. Ding /The journal of immunology)


Some types of cells are the connecting link between innate and acquired immune systems. The response created by the innate immune system subsides with infection. On the other hand, once adaptive immunity is created against a particular infection then it lasts forever.

Related | COVID-19: Everything You Need Know About Coronavirus

If you wanted to know more about the immune system you may watch the below video. The video will explain the complexity of the immune response.



What is a vaccine?

A vaccine is a type of medicine that trains the body’s immune system so that it can fight disease it has not come into contact with before. Vaccine mainly consists of weakened or killed forms of the pathogen, its toxins, or one of its surface proteins or antigen.

Scientists divided vaccines into 4 categories –

  • Live-attenuated vaccines
  • Inactivated vaccines
  • Subunit, recombinant, polysaccharide, and conjugate vaccines
  • Toxoid vaccines 


Live-attenuated Vaccines

It contains a weakened form of the pathogen and attenuation is carried out by the use of chemicals or heat. Such type of vaccines develops strong, long term immunity against a particular infection. There are some limitations to such types of vaccines. The vaccine should be stored and transported at low temperatures. Peoples with low immunity should talk to medical professionals before taking vaccines as it contains live pathogen. Examples of this type of vaccine are Measles, mumps, rubella (MMR combined vaccine), Rotavirus, Smallpox, Chickenpox, Yellow fever.


Inactivated Vaccines

It contains the completely dead pathogen of disease. This type of vaccine provides good immunity but not as great as live attenuated vaccines. It is necessary to take several doses to get strong immunity against the particular pathogen. This type of vaccine protects against Hepatitis A, Flu, Polio, Rabies.


Subunit, Recombinant, Polysaccharide, and Conjugate Vaccines

This type involves particular parts of a pathogen like protein, polysaccharides ( sugars ), or capsid (an outer member of some microorganisms). The main advantage of such vaccines is that it can be used by everyone even if a person is immunocompromised (weak immune system). Also, it provides a strong immune response. Sometimes it is necessary to take booster shots for getting lifelong immunity. These are the following diseases against which such type of vaccine can be used.

  • Hib (Haemophilus influenzae type b) disease, Hepatitis B
  • HPV (Human papillomavirus)
  • Whooping cough, Pneumococcal disease, Meningococcal disease, Shingles


Toxoid Vaccines

The toxoid vaccine is made from toxins obtained from pathogens. In this type of vaccine, immune responses are generated against toxins and not for the pathogen. Like some other types of vaccines, you may need booster shots to get protection against diseases. These types of vaccines are used against Diphtheria and Tetanus.


Mode of Action of a Vaccine

The antigen is a molecule present on the surface of the pathogen. The presence of antigens in the body activates the immune system against the pathogen. As part of the immune response, antibodies are made against the pathogen. Antibody guides complement cascade to fight with pathogens. Complement cascade involves phagocytosis, inflammation, and members attack which is also called the primary response. It triggers the following immune functions:

  • Phagocytosis – by opsonizing antigens.
  • Inflammation – by attracting macrophages and neutrophils
  • Membrane attack – by rupturing the cell wall of bacteria.

There are two types of memory cells present in the body (T-cells and B-cells) which replicate during infection and remain in the body. Those memory cells get active as it detects antigen which had previously encountered. Once antibodies are made for a pathogen then that pathogen won’t infect that particular person anymore.

(Image Credits: Sunita Awate1,2, Lorne A. Babiuk3, and George Mutwiri /frontiers)

When vaccines enter the body it activities our immune system. As vaccines contain either weakened pathogens or antigens then our adaptive immune system starts producing antigens along with memory cells. During all these processes humans don’t get harmed as it happens during natural infection.

Also, this immunity lasts lifelong. The only thing which needs to be taken care of is a side effect vaccine. Many clinical trials are carried out to study the effectiveness of the vaccine. That’s the reason why it takes so long time to develop a vaccine.


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