What is the basic principle behind vaccine development? How do vaccines work? What approaches were adopted by the Indian vaccine…

The basic principle of vaccination is the induction of acquired immunity by presenting a harmless antigen—such as an inactivated pathogen, protein subunit, or genetic material—to the immune system to stimulate protective immunological memory without causing clinical disease.

Mechanism of Action

Once introduced, antigen-presenting cells (APCs) capture and display the vaccine antigen to helper T-cells. This triggers a dual immune response: B-cells are activated to differentiate into plasma cells that produce pathogen-specific neutralizing antibodies, while cytotoxic T-cells are primed to destroy infected host cells. Crucially, a subset of these lymphocytes transforms into long-lived memory B and T cells. Upon subsequent exposure to the actual pathogen, these memory cells mount an immediate, high-affinity immune attack, neutralizing the infection before it causes disease.

Approaches Adopted by Indian Manufacturers

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

Inactivated Whole-Virion Platform: Bharat Biotech, in collaboration with the Indian Council of Medical Research (ICMR) and the National Institute of Virology (NIV), developed Covaxin. It utilized chemically inactivated SARS-CoV-2 virions cultured on Vero cells, presenting the complete viral structure to generate broad immunity.

Viral Vector Platform: The Serum Institute of India (SII) partnered with Oxford-AstraZeneca for technology transfer to produce Covishield. It uses a replication-deficient chimpanzee adenovirus (ChAdOx1) vector to deliver the genetic sequence of the spike protein into host cells.

Plasmid DNA Platform: Zydus Cadila developed ZyCoV-D, India's first indigenous plasmid DNA vaccine, utilizing a needle-free applicator to introduce non-replicating DNA plasmids encoding the spike protein.

Protein Subunit and mRNA Platforms: Biological E's Corbevax used a recombinant receptor-binding-domain protein, while Gennova's GEMCOVAC became India's first mRNA vaccine.

These diverse approaches highlighted India’s strong indigenous R&D and technology-absorption capacities, advancing the goals of Atmanirbhar Bharat while bolstering global vaccine equity through COVAX and the Vaccine Maitri initiative.