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 of vaccine development

• Identify an antigen (protein, sugar, whole killed microbe, or genetic code for that protein) that is immunogenic but not pathogenic in the form given.
• Combine it with a platform: live attenuated, inactivated whole virus, subunit/protein, toxoid, viral vector, or nucleic acid (mRNA/DNA).
• Add adjuvants where needed so the innate system notices the antigen.
• Prove safety, immunogenicity and efficacy in phased clinical trials, then pharmacovigilance after approval.
• Manufacture under GMP, cold chain, and strain update when the pathogen evolves (influenza yearly; COVID boosters as variants rose).
• Ethics: informed consent, and correlates of protection when efficacy trials become hard.

How vaccines work

• Innate cells at the injection site take up antigen and present it to T cells in lymph nodes.
• B cells make antibodies that can neutralise the pathogen; memory B and T cells remain after the shot.
• On later exposure, memory cells respond faster and stronger, preventing disease or reducing severity.
• Vaccines do not typically ‘cause the disease’ when inactivated, subunit, vector (non-replicating) or mRNA; live attenuated vaccines use a weakened organism and have specific contraindications.
• Herd effects appear when enough people have memory that transmission falls; they are a population result, not a promise to one unvaccinated person.

Indian COVID-19 approaches

• Covishield: Serum Institute of India manufacture of the Oxford–AstraZeneca chimpanzee adenovirus vector carrying the SARS-CoV-2 spike gene. Non-replicating vector; spike protein is produced in the vaccinee’s cells.
• Covaxin (BBV152): Bharat Biotech with ICMR–NIV; inactivated whole virion plus alum-like adjuvant (Alhydroxiquim-II). Traditional kill-and-inject logic, indigenous strain work.
• Other Indian lines included protein subunit (for example Corbevax-type receptor-binding domain), DNA (ZyCoV-D, first plasmid DNA COVID vaccine authorised in India), and later mRNA and nasal candidates in development or limited use.
• National rollout: CoWIN, staggered age groups, and later precaution doses; mix-and-match was studied as evidence evolved.
• Public communication must stay factual: vaccines cut severe disease and death; they are not a 100 per cent shield against all infection, especially as variants changed.

Principle illustrated

• Vector and inactivated platforms are two validated answers to the same principle: present spike (or the whole virus) without COVID disease, then rely on memory.