What is the basic principle behind vaccine development? How do vaccines work? What approaches were adopted by the Indian vaccine manufacturers to produce COVID-19 vaccines?

Sample Answer


A vaccine is a biological preparation that improves immunity to a particular disease.


The principle of vaccination is to induce protection against a pathogen by mimicking its natural interaction with the human immune system. To achieve this, the vaccine must contain antigens that are either derived from the pathogen or produced synthetically to represent components of the pathogen. Vaccines can be said to use ‘memory’ of the immune system.

Working of vaccine

  • Recognition: Vaccination works by recognising new antigens.
  • Producing antibodies:  B-cells act as antigen producing factories. 
  • Builds adaptive immune system: Once the vaccinated body is left with a supply of T-lymphocytes and B-lymphocytes that will remember how to fight that disease.
  • Memory creation: After the threat has passed, many of the antibodies will break down, but immune cells called memory cells remain in the body. 

Approaches adopted by the Indian vaccine manufacturers to produce COVID-19 vaccines

In the initial phase of COVID-19, The Drug Controller General of India (DCGI) has granted the emergency-use approval for two indigenous vaccines: COVISHIELD by Serum Institute of India and COVAXIN by Bharat Biotech.

Covaxin is an inactivated vaccine whereas Covishield is a live vaccine. Live Vaccines use a weakened (or attenuated) form of the germ that causes a disease. Inactivated vaccines use active pathogens, killed either by a chemical or heat. Although the pathogen is killed, or made to lose its reproduction capacity, various parts of the pathogen are intact.

  • Corbevax – is a protein subunit vaccine, using a harmless Spike (S) protein.
  • Covavax – Recombinant Nanoparticle Vaccine


The vaccine reduces the risk of complications and mortality following subsequent exposure to an infectious agent. 

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