How Do Vaccines Work?
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How Do Vaccines Work?

Vaccines are supposed to be protecting us from several infectious diseases. This article describes the way vaccines work.

A vaccine is a non-pathogenic biological preparation that provides immunity towards specific infectious diseases. The preparation can either be killed or live and weakened forms of pathogens, or purified components such as proteins. Vaccination has been proved to be an effective method of preventing many viral and bacterial diseases. All vaccinations function on the principal of introducing the disease causing pathogens into the immune system in order to evoke an immune response by developing antibodies for those pathogens or antigens. These antibodies help the vaccine recipient to efficiently fight the pathogenic disease if and when it occurs. Antigens are chemical substances having the ability to stimulate the body to produce an antibody. Antibodies are chemical substances that react with the specific antigens and help the body in fighting against diseases. Antibodies play an important role in the defense mechanisms of the body. In generic terms, the immune system produces antibodies in response to the presence of the corresponding antigen.

A vaccine may be administered orally, or by intramuscular, intradermal or subcutaneous injection.


Types of Vaccines

The four basic types of vaccines used are:

  • Killed or weakened vaccines: The pathogenic virus is chemically treated and rendered non-pathogenic. The virus is either killed or weakened by treating with heat, formalin et cetera.
  • Attenuated vaccines: The live pathogenic virus is clinically altered or mutated and rendered non-pathogenic. The mutation makes the virus weak and hence these live viruses grow in the host or vaccine recipient but fail to cause the disease.
  • Sub-unit vaccines: Sub-unit vaccines contain purified components extracted from the pathogenic virus. The extracted components do not contain the viral or disease causing portion of the virus.
  • DNA vaccines: Genetic material from a pathogenic virus is combined with another usually harmless virus.


The number of different antigens contained in the vaccine is termed as the Valence of the vaccine. Based on the Valence, vaccines are categorized as:

  • Monovalent or Univalent: Monovalent vaccines contain single strain of antigens and these are used to immunize against a single antigen.
  • Multivalent or Polyvalent: Multivalent vaccines contain two or more strains of the same antigen or, two or more different antigens. These vaccines are used to immunize against a group of closely related diseases.



A vaccine contains dead, weakened or clinically altered antigens that stimulate the vaccine recipient’s body to produce antibodies. For example, a vaccine for polio will typically contain a dose of the inactivated poliovirus. These dead or weakened microorganisms will be recognized as foreign particles by the leukocytes (white blood cells) of the vaccine recipient’s body. However, the microorganisms will not cause the disease as they have been inactivated. While the leukocytes learn to fight against these pathogens, the vaccine recipient will display symptoms of the disease, such as high fever, vomiting etc. Once the leukocytes understand the structure and composition of the microorganisms, they start producing antibodies to fight the microorganisms. These antibodies are like memory cells of the immune system. Any future invasion of the polio virus will be immediately taken care of by these antibodies. The leukocytes would not take time to understand the antigens. Instead they will produce the needed antibodies immediately, thus preventing the virus from causing the disease.

To sum it up, the introduced antigens stimulate the vaccine recipient’s immune system to recognize the antigens as foreign substance, destroy them, and remember them in case of any future infections. The vaccine recipient now develops immunity against that strain of antigen.

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Comments (3)

Outstanding work.

Well presented.

Excellent educational info. Promoted