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Vaccines - An Overview

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Vaccines are simple and effective ways that guide the immune system to produce antibodies against and in response to antigens. Read the article to know more.

Medically reviewed by

Dr. Kaushal Bhavsar

Published At October 7, 2022
Reviewed AtNovember 1, 2023


A vaccine is a biological suspension used to stimulate the production of antibodies to provide immunity against diseases. They are made up of various constituents that make them more effective and efficient. A vaccine typically contains an agent that resembles disease-causing microorganisms and is often made from killed or weakened forms of microbes. The agent stimulates the body's immune system to recognize foreign microbes and destroy them. The vaccines are administered to an individual only after approval through clinical trials.

What Are Vaccines?

The vaccine is a suspension of killed, fragmented or weakened microorganisms of biological preparation consisting of lymphocytes (white blood cells that help to control immune response) antibodies or messenger RNA (mRNA) administered in the primary stage to prevent disease. A British physician named Edward Jenner, in the year 1796, used the cowpox virus to protect against smallpox. Later, the French microbiologist Louis Pasteur 1885 developed the first vaccine against rabies (the virus transmitted to humans through an animal bite). The vaccine provides immunization to the body. It is a procedure to stimulate an immune response through active vaccination. They are in the form of pills, liquids, nasal sprays, or injections.

What Are Constituents of Vaccine?

A vaccine is made of constituents that involve the following components.

  • Antigen: It is a weakened or killed form of live bacteria or virus that guides our body to recognize and fight against diseases.

  • Stabilizers: Helps to protect the transportation and storage of the vaccine.

  • Preservatives: These are present to prevent contamination and protection of vaccines from external bacteria and viruses, for example-Thimerosal.

  • Adjuvants: These are present that help in boosting the immune system. For example, an aluminum solvent is usually used as an adjuvant.

What Do the Different Types of Vaccines Depend Upon the Constituent?

  • Live Attenuated Vaccines: It is a weakened form of the virus. Examples are chickenpox, measles, mumps, and rubella virus.

  • Inactivated Vaccine: It is made by using killed microorganisms. For example, the polio vaccine.

  • Toxoid Vaccines: Uses toxic products or inactivated bacterial toxins made by microorganisms, for example, diphtheria and tetanus vaccines.

  • Recombinant Viruses: These are formed through genetic engineering- for example, the Human papillomavirus (HPV) vaccine.

  • Conjugate Virus: Consists of antigen-coated polysaccharides. Examples include the Hib vaccine (Haemophilus influenzae type B).

  • Subunit Vaccines: These are made up of specific proteins. Human papillomavirus (HPV) and hepatitis B are examples of subunit vaccines.

  • mRNA Vaccine: Uses messenger RNA.

  • Viral Vector Vaccines: Uses genetic material that is instructed to make specific proteins. It is commonly used in veterinary medicine.

  • Biosynthetic Vaccine: Consists of a man-made substance similar to bacteria or virus.

What Are Commonly Used Vaccines?

The commonly used vaccines are as follows:

  • Measles vaccine.

  • Rubella vaccine.

  • Mumps vaccine.

  • Chickenpox vaccine.

  • Human papillomavirus vaccine (HPV vaccine).

  • Tetanus vaccine.

  • Diphtheria vaccine.

  • Polio vaccine.

  • Influenza vaccine.

  • Meningococcal vaccine.

  • Rotavirus vaccine.

  • Shingles vaccine.

  • Haemophilus influenzae type B (Hib) vaccine.

  • Pneumococcal polysaccharide vaccine.

  • Pneumococcal conjugate vaccine.

  • Covidshield vaccine.

  • Hepatitis A vaccine.

  • Hepatitis B vaccine.

  • Hepatitis E vaccine.

  • Dengue fever vaccine.

  • Anthrax vaccine.

  • Adenovirus fever.

  • Japanese encephalitis fever.

  • Typhoid vaccine.

  • Yellow fever vaccine.

  • Covidshield vaccine.

  • Tuberculosis vaccine.

  • Tick-borne encephalitis vaccine.

  • Diphtheria-tetanus-pertussis vaccine (DTaP vaccine).

What Is the Mechanism of Action of the Vaccine?

  • Our immune system consists of cells, tissues, and organs that work together to invade the infection.

  • Bacterial and virus cells in our body are marker cells known as antigens. Antigens can induce changes in the immune system and cause damage.

  • When the vaccine is introduced into the body, it guides the immune system to produce antibodies against the antigens.

  • Vaccines consist of inactivated or weakened forms of the virus or bacteria in the body. Lymphocytes are white blood cells of the immune system, that become active whenever foreign protein comes in contact with the antigen.

  • When foreign microbes invade the human body, the immune system starts triggering a series of responses to identify and remove them from the body. The foreign microbes introduce antigens into the body.

  • Coughing, inflammation, sneezing, and fever occur as a means of protection by the immune system. Special cells such as B and T cells are responsible for fighting against the microbes by creating memory cells as a response. B-lymphocytes are defensive white blood cells that produce antibodies against microbes, while T-lymphocytes are memory cells that recognize the familiar germ to which the body was exposed previously. These immune cells recognize foreign invaders and produce specific antibodies.

How Are Vaccines Approved for Use?

Before administering a new vaccine to the general population, specific investigations and approvals are carried out to ensure that it is safe and effective. Every vaccine, before administration, goes through the development, testing, and monitoring process to ensure its effective working and safe use. The development phase has three further substages:

  1. Exploratory - In which the researchers investigate the antigen.

  2. Preclinical - It is the preclinical phase, in which testing is done on animals to determine vaccine effectiveness.

  3. Application - The application phase involves the investigation of the new drug by the researchers.

After the development phase, the vaccine passes through preclinical trials in three phases to get approved.

  • Phase 1 - This trial includes a small group of people ranging from one to ten.

  • Phase 2 - After the approval of the first phase, the vaccine is administered to hundreds of people, and this phase is called phase 2 clinical trials.

  • Phase 3 - Finally, the phase 3 trial is carried out among thousands of people after the phase 2 trial is approved. The population who received the vaccine is then monitored to determine whether any risk factor is present and to check its outcome.

Which Is the Latest Vaccine Developed in India?

The latest vaccine in India introduced is the vaccine for covid. The government approves two vaccines.

  • Covishield: It is manufactured in India by the Serum Institute of India.

  • Covaxin: It is manufactured by Bharat Biotech in collaboration with ICMR in India.


Vaccines are a blessing to humans as they protect them from various diseases. They are not the cure for any disease but are preventive actions for all diseases. They provide us with long-lasting immunity. They have the potential to showcase humoral immunity (antibody-mediated immunity that can produce antibodies against a specific antigen) as well as cellular immunity (an immune response that does not involve antibody production but instead activates the antigen-specific cells). They are easy to handle and cost-effective. Vaccines have reduced the number of deaths caused by diseases such as diphtheria, measles, and polio. Some of the vaccines require multiple administration of doses after weeks, months, or years. This allows for the production of long-lived antibodies and memory cell development. In the case of a few vaccines, they become ineffective over time; for them, the booster doses must be administered after some time.

Dr. Kaushal Bhavsar
Dr. Kaushal Bhavsar

Pulmonology (Asthma Doctors)


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