What is the basic principle behind vaccine development? How do vaccines work? What approaches were adopted by the Indian vaccine manufactures to produce COVID-19 vaccines? UPSC CSE Main 2022 GS Paper 3
The basic principle of vaccine development is to stimulate the immune system to produce antibodies against a specific disease-causing organism, without causing the actual disease. This way, the body can remember the organism and fight it off quickly if it encounters it again in the future.
Vaccines work by introducing a tiny fragment of the organism (the antigen) or the blueprint for making the antigen into the body, usually by injection. The antigen triggers an immune response, in which the body produces white blood cells and antibodies that can recognize and destroy the organism. Some of these cells and antibodies remain in the body as memory cells, which can rapidly respond to a future infection by the same organism.
There are different types of vaccines, depending on how the antigen is prepared or delivered. Some of the common types are:
Live attenuated vaccines: These vaccines contain a weakened form of the whole organism, which can still replicate but does not cause disease. Examples are measles, mumps, rubella (MMR) and chickenpox vaccines.
Inactivated vaccines: These vaccines contain a killed form of the whole organism, which cannot replicate but can still elicit an immune response. Examples are polio, hepatitis A and rabies vaccines.
Subunit vaccines: These vaccines contain only a part of the organism, such as a protein or sugar, that is essential for its identity and function. Examples are hepatitis B, human papillomavirus (HPV) and pertussis vaccines.
Conjugate vaccines: These vaccines link a subunit antigen to another molecule that can enhance its immunogenicity, such as a polysaccharide or a protein. Examples are Haemophilus influenzae type b (Hib), meningococcal and pneumococcal vaccines.
Toxoid vaccines: These vaccines contain an inactivated form of a toxin produced by the organism, which can cause disease even without the presence of the organism. Examples are tetanus and diphtheria vaccines.
Recombinant vector vaccines: These vaccines use a harmless virus or bacterium as a carrier to deliver the genetic material of the antigen into the cells, where it can be expressed and trigger an immune response. Examples are Ebola and COVID-19 (Sputnik V) vaccines.
mRNA vaccines: These vaccines use messenger RNA (mRNA) molecules that encode the antigen, which can be translated into proteins by the cells and stimulate an immune response. Examples are COVID-19 (Pfizer-BioNTech and Moderna) vaccines.
DNA vaccines: These vaccines use plasmids (circular DNA molecules) that encode the antigen, which can be taken up by the cells and transcribed into mRNA and then proteins. Examples are COVID-19 (ZyCoV-D) and malaria (PfSPZ) vaccines.
In India, there are currently four COVID-19 vaccines that have been approved for emergency use:
Covishield: This is an inactivated vaccine that contains a modified version of adenovirus 5 (a common cold virus) that carries the gene for the spike protein of SARS-CoV-2 (the virus that causes COVID-19). It was developed by Oxford University and AstraZeneca, and is manufactured by Serum Institute of India under license.
Covaxin: This is an inactivated vaccine that contains whole killed SARS-CoV-2 viruses that have been treated with chemicals to render them harmless. It was developed by Bharat Biotech in collaboration with Indian Council of Medical Research (ICMR) and National Institute of Virology (NIV).
Sputnik V: This is a recombinant vector vaccine that uses two different adenoviruses (Ad26 and Ad5) as carriers for the gene for the spike protein of SARS-CoV-2. It was developed by Gamaleya Research Institute of Epidemiology and Microbiology in Russia, and is manufactured by Dr. Reddy's Laboratories in India under license.
ZyCoV-D: This is a DNA vaccine that uses plasmids that encode the gene for the spike protein of SARS-CoV-2. It was developed by Zydus Cadila, and is the first COVID-19 vaccine to be approved for children aged 12 years and above in India.
Other COVID-19 vaccines that are undergoing clinical trials in India include:
Corbevax: This is a subunit vaccine that contains the recombinant spike protein of SARS-CoV-2. It was developed by Biological E in collaboration with Baylor College of Medicine and Dynavax Technologies.
GEMCOVAC-OM: This is an mRNA vaccine that is designed to target the Omicron variant of SARS-CoV-2. It was developed by Gennova Biopharmaceuticals with support from Department of Biotechnology (DBT) and Biotechnology Industry Research Assistance Council (BIRAC).
BBV154: This is a nasal vaccine that delivers the inactivated SARS-CoV-2 virus to the mucosal lining of the nose, where it can induce both local and systemic immunity. It was developed by Bharat Biotech.
HGCO19: This is an mRNA vaccine that encodes the spike protein of SARS-CoV-2. It was developed by Hetero Biopharma.