What is the basic principle behind vaccine development? How do vaccines work? What approaches were adopted by Indian vaccine manufacturers to produce COVID-19 vaccines? (Answer in 250 words)

Vaccination trains adaptive immunity by exposing the body to a safe antigen or genetic instruction, generating antibodies, memory B cells and T cells without causing the target disease.

Principle and mechanism

• Antigens from an inactivated organism, protein, vector or nucleic acid are presented to immune cells.
• The primary response creates immune memory; later exposure produces a faster and stronger response that prevents severe disease.
• Adjuvants can enhance immune activation, while boosters sustain protection as immunity wanes or variants evolve.

Indian approaches to COVID-19 vaccines

• Covaxin used an inactivated whole-virion platform with an adjuvant, requiring conventional cold-chain handling.
• Covishield used a non-replicating adenoviral vector encoding the spike protein and was manufactured through technology transfer.
• ZyCoV-D used a DNA-plasmid platform delivered by a needle-free system.
• Other Indian efforts explored recombinant protein, mRNA and intranasal approaches, reflecting platform diversification.

Significance

• Domestic production improved supply resilience, supported the vaccination programme and enabled exports. Regulatory review, clinical trials, pharmacovigilance, informed consent and transparent communication remain essential.

Antigen; adaptive immunity; memory cells; inactivated vaccine; viral vector; DNA vaccine; adjuvant; pharmacovigilance.