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

 The basic principle behind vaccine development is to stimulate the immune system to recognize and fight specific pathogens, such as viruses or bacteria. Vaccines work by introducing a harmless part of the pathogen (e.g., antigens, weakened or inactivated pathogens, or genetic material) into the body. This stimulates the immune system to produce an immune response, including the production of antibodies and memory cells. If the person is later exposed to the actual pathogen, their immune system can recognize and quickly mount a response, preventing or reducing the severity of the infection.

In the case of COVID-19 vaccines developed by Indian manufacturers, they adopted various approaches:

1. Inactivated Virus Vaccines: Bharat Biotech developed Covaxin, an inactivated virus vaccine. This vaccine involves growing the SARS-CoV-2 virus in culture and then inactivating it using heat, chemicals, or radiation. The inactivated virus is used as the antigen to stimulate an immune response.

2. Viral Vector Vaccines: The Oxford-AstraZeneca vaccine, known as Covishield in India, is based on a viral vector approach. It uses a modified chimpanzee adenovirus as a vector to deliver the genetic material of the SARS-CoV-2 spike protein into cells. This genetic material instructs the cells to produce the spike protein, triggering an immune response.

3. Protein Subunit Vaccines: Biological E and Novavax collaborated to develop Covovax, a protein subunit vaccine. This vaccine utilizes a part of the spike protein of SARS-CoV-2, specifically the receptor-binding domain (RBD). The RBD is produced using recombinant DNA technology and acts as the antigen to elicit an immune response.

4. mRNA Vaccines: The mRNA-based vaccine, Covishield, developed by Pfizer-BioNTech, also known as Comirnaty, and Moderna's mRNA-1273, have been authorized for emergency use in India. These vaccines contain a small piece of mRNA that encodes the spike protein of SARS-CoV-2. Once inside the cells, the mRNA instructs the cells to produce the spike protein, leading to an immune response.

These different vaccine approaches share the common goal of stimulating the immune system to recognize and respond to SARS-CoV-2. They have undergone rigorous testing and regulatory approvals to ensure safety, efficacy, and quality before being authorized for vaccination campaigns.