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 ?

The elimination of deadly diseases like Polio & Smallpox have been made possible through the advent of vaccines.

Vaccines work on the principle of acquired immunity. They introduce the disease-causing germ (Antigen) which makes the body manufacture Antibodies to kill the foreign particle. At the same time, memory cells are produced which remember the antigen (its protein structure). Whenever the body comes in contact with the antigen (or its similar cousins), it initiates an immune response. This

either prevents infection altogether or makes the symptoms less intense.

TYPES OF VACCINES

The different types depend on the method of introduction of antigen in the body:

1. Attenuated Live Virus Vaccines: Virus itself introduced, but after dampening its effects.
2. Inactivated (Dead) Vaccines: Dead sample of the virus is introduced.
3. Viral vector vaccines: Another harmless virus (usually adenovirus) used as carrier. Eg. Covishield.
4. Subunit vaccines: Not the whole virus, but subunits (mRNA or DNA) introduced -> body itself tricked into manufacturing the virus (through encoding of mRNA or DNA). Eg. Pfizer.