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 ?

According to WHO vaccination is a simple, safe, and effective method of protecting individuals against dangerous diseases before they are exposed to them.”

Principle of vaccination:

• Vaccines stimulate the immune response (T-cells and B-cells together work) to recognise a pathogen (a disease-causing organism) or part of a pathogen. 
• It induces protection against a pathogen by mimicking its natural interaction with the human immune system.

Vaccines Work:

1. When the vaccine is introduced into the body, the white blood cells come in the response. 
2. The WBCs recognise the vaccine as foreign substance by the surface molecule on the vaccine. 
3. After recognition the B and T cells start dividing rapidly. 
4. T-cytotoxic and B killer cells started responding to the vaccine. That's why fever is common after vaccination. 
5. Some WBCs differentiate as B- memory cells which are stored within the body. 
6. When the pathogen attack takes place or is given a booster dose, the B-memory cells start giving faster reaction as the body has accepted the surface particle as foreign previously. 

COVID-19 Vaccines by Indian Manufactures:

• Covaxin (Bharat Biotech): They contain dead, inactivated forms of virus, incapable of infecting people. Inactivated vaccines do not replicate and are therefore unlikely to revert and cause pathological effect, but still able to instruct the immune system to mount a defensive reaction against an infection. 
• Covishield (SII with Oxford University): is a recombinant non-replicating virus which is genetically engineered to produce coronavirus proteins in the body, but the virus is weakened and cannot cause the disease. 
• iNCOVACC (Bharat Biotech): is a non-replicating viral vector-based vaccine. Novel kind of Nasal vaccine works by suppressing the broad immune response of the virus in nasal cavity by neutralising IgG antibodies suppressing mucosal IgA antibodies and T cell response. 
• Gemcovac-19(Pune-based Gennova Biopharmaceutical): Messenger RNA (mRNA) vaccines teach our cells how to make a protein that will trigger an immune response inside our bodies. After vaccination, the mRNA will enter the muscle cells.

Vaccination is a simple, safe, and effective way of protecting people against harmful diseases, before they come into contact with them.