Q.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?

Body Analysis

Basic Principle Behind Vaccine Development

The fundamental principle of vaccination is immunological memory. The vaccine introduces a harmless, non-pathogenic form of an antigen (a virus, bacterium, or part of it) to the immune system. This trains the body to produce specific antibodies and memory cells, ensuring a rapid and robust defense if the actual pathogen is encountered in the future.

How Vaccines Work

1. Antigen Presentation: The vaccine introduces the antigen into the body.
2. Immune Activation: Specialized immune cells (APC) present the antigen to T-cells and B-cells.
3. Antibody Production: B-cells synthesize specific antibodies tailored to neutralize the target antigen.
4. Memory Cell Formation: Once the mock infection is cleared, a pool of memory B and T-cells persist in the body for years, ready to neutralize the real virus upon exposure.
5. Herd Immunity: When a large portion of the population is vaccinated, the spread of the disease is restricted, protecting vulnerable individuals who cannot be immunized.

Approaches Adopted by Indian Vaccine Manufacturers for COVID-19

Indian manufacturers adopted diverse scientific platforms to develop and produce COVID-19 vaccines:

1. Inactivated Pathogen Approach (Covaxin - Bharat Biotech)

• Mechanism: Developed in collaboration with ICMR, Covaxin uses a whole-virion inactivated SARS-CoV-2 virus.
• The live virus was chemically inactivated using Beta-propiolactone, rendering it unable to replicate, while keeping the surface proteins intact to trigger an immune response.

2. Viral Vector Approach (Covishield - Serum Institute of India)

• Mechanism: Manufactured under license from Oxford-AstraZeneca, Covishield utilizes a modified, non-replicating chimpanzee adenovirus vector.
• This vector carries the genetic code for the SARS-CoV-2 spike protein into human cells, prompting them to produce the spike protein and trigger an immune response.

3. DNA-Based Approach (ZyCoV-D - Zydus Cadila)

• Mechanism: This was the world's first plasmid DNA vaccine approved for human use.
• It introduces a plasmid DNA ring containing the gene for the spike protein. Once inside host cells, the DNA is transcribed to produce the spike protein, inducing immunity. It is delivered needle-free.

4. Protein Subunit Approach (Corbevax - Biological E)

• Mechanism: Corbevax is a recombinant protein subunit vaccine.
• Instead of introducing a virus or genetic material, it directly delivers lab-grown, purified spike proteins of the SARS-CoV-2 virus combined with an adjuvant to boost the immune response.

5. Heterologous Adenovirus Vector (Sputnik V - Manufactured under license)

• Mechanism: Produced by Indian firms like Dr. Reddy's, it uses two different human adenovirus vectors (Ad26 and Ad5) for the first and second doses to prevent the body from developing immunity against the vector itself, enhancing efficacy.