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 ?

Basic Principle Behind Vaccine Development

The core principle of vaccine development revolves around the concept of ‘immunological memory’. Vaccines introduce antigens – substances that trigger an immune response – into the body. These antigens can be weakened or inactivated pathogens, or parts of pathogens like proteins or genetic material. This exposure prompts the immune system to produce antibodies and activate immune cells (like T-cells) that specifically recognize and neutralize the pathogen. Crucially, the immune system ‘remembers’ this encounter, allowing for a faster and more effective response upon subsequent exposure to the actual pathogen, preventing or mitigating the disease.

How Vaccines Work

Vaccines function by mimicking a natural infection, but without causing illness. Different types of vaccines employ varying strategies:

• Live-attenuated vaccines: Use a weakened form of the pathogen. They create a strong and long-lasting immune response but aren’t suitable for everyone (e.g., measles, mumps, rubella).
• Inactivated vaccines: Use a killed version of the pathogen. They are safer than live vaccines but often require multiple doses (e.g., polio, influenza).
• Subunit, recombinant, polysaccharide, and conjugate vaccines: Use specific parts of the pathogen, like proteins or sugars, to trigger an immune response (e.g., Hepatitis B, HPV).
• Toxoid vaccines: Use inactivated toxins produced by the pathogen (e.g., tetanus, diphtheria).
• mRNA vaccines: A newer technology that delivers genetic instructions for the body to produce a viral protein, triggering an immune response (e.g., Pfizer-BioNTech, Moderna COVID-19 vaccines).
• Viral Vector vaccines: Use a harmless virus to deliver genetic material from the target pathogen into cells, prompting an immune response (e.g., AstraZeneca-Oxford, Johnson & Johnson COVID-19 vaccines).

Approaches Adopted by Indian Vaccine Manufacturers for COVID-19 Vaccines

Indian vaccine manufacturers played a pivotal role in the global fight against COVID-19, adopting diverse approaches:

• Covishield (Serum Institute of India - SII): Utilized the viral vector platform, based on the AstraZeneca-Oxford vaccine. SII scaled up production to meet domestic and global demand, employing technology transfer and leveraging existing manufacturing infrastructure.
• Covaxin (Bharat Biotech): Developed an inactivated whole-virus vaccine, using a traditional vaccine development approach. This involved growing the virus in cell cultures and then inactivating it. Covaxin faced initial scrutiny but demonstrated efficacy and safety in clinical trials.
• Covovax (Serum Institute of India - SII): A protein subunit vaccine developed in collaboration with Novavax. This vaccine uses a recombinant protein of the SARS-CoV-2 spike protein to elicit an immune response.
• ZyCoV-D (Zydus Cadila): Developed a DNA plasmid vaccine, the first DNA vaccine approved for emergency use in India. This technology delivers genetic material directly into cells to produce the viral protein.

These manufacturers faced challenges including rapid scaling of production, ensuring supply chain resilience, navigating regulatory approvals, and addressing vaccine hesitancy. The Indian government provided financial support and facilitated technology transfer to accelerate vaccine development and production.

Table: Comparison of Indian COVID-19 Vaccines

Vaccine Name	Manufacturer	Technology Platform	Efficacy (approx.)
Covishield	Serum Institute of India	Viral Vector	70-80%
Covaxin	Bharat Biotech	Inactivated Virus	78%
Covovax	Serum Institute of India	Protein Subunit	89%
ZyCoV-D	Zydus Cadila	DNA Plasmid	66.6%