Vaccine Development: Principles, Mechanism and India’s COVID-19 Approach

A vaccine gives the body a safe first meeting with a germ. The real germ then meets an immune system that is ready.

How does the body respond?

• The part of a germ that makes the body form antibodies is called an antigen.
• Each antibody is trained to recognise one specific antigen.
• At the first meeting, the body takes time to make antibodies. A person can fall ill in that gap.
• The body also makes memory cells that stay alive after the germ is beaten.
• At a later meeting with the same germ, the antibody response is much faster and stronger.

What is the memory hook?

Think “antigen, antibody, memory”. Meet, make, remember.

Vaccines differ in what they put into the body. A January 2021 government briefing listed four kinds. India made a fifth.

Which kinds matter for exams?

• Inactivated: the whole germ is killed. Covaxin is of this kind.
• Viral vector: a harmless virus carries a gene. Covishield and Sputnik V are of this kind.
• Protein subunit: only a protein piece is used. Corbevax is of this kind.
• mRNA: genetic instructions are used. Pfizer-BioNTech and Moderna are of this kind.
• DNA: a plasmid carries the gene for the spike protein. ZyCoV-D is of this kind.

What is the memory hook?

Think “killed, carried, piece, message, plasmid”.

India authorised two vaccines first. They work in different ways.

What are the key facts?

• Covishield and Covaxin both received Emergency Use Authorization in India by 12 January 2021.
• The PIB briefing said the Serum Institute of India supplied Covishield.
• Covaxin is a Bharat Biotech vaccine. One dose has 6 micrograms of whole-virion inactivated SARS-CoV-2 antigen.
• It also holds aluminium hydroxide gel and a TLR 7/8 agonist to help the immune response.
• Covishield is ChAdOx1 nCoV-19, a recombinant vaccine. Its vector is a replication-deficient chimpanzee adenovirus that carries the spike gene.
• Covishield is made in genetically modified human embryonic kidney (HEK) 293 cells.

What is the memory hook?

Think “Covaxin kills, Covishield carries”.

These two came later. Both were backed by the Department of Biotechnology.

What are the key facts?

• Zydus Cadila got emergency approval for ZyCoV-D from the Drug Controller General of India (DCGI) on 20 August 2021.
• It was described as the world’s first DNA-based COVID-19 vaccine. It was approved for people aged 12 and above.
• It was made with the Department of Biotechnology (DBT) under Mission COVID Suraksha, and BIRAC ran it.
• It is a three-dose vaccine. It makes the spike protein of the virus in the body.
• Interim phase III results in over 28,000 volunteers showed efficacy of 66.6% for symptomatic RT-PCR positive cases.
• Corbevax, from Biological E, is India’s first home-made protein sub-unit vaccine. It uses the receptor binding domain (RBD) of the spike protein.
• It has CpG 1018 and alum as adjuvants. It is a two-dose shot, kept at 2 to 8 degrees Celsius.
• The DCGI approved it for adults on 28 December 2021, and later for ages 12 to 18.

What is the memory hook?

Think “Zydus DNA, three doses; Biological E protein, two doses”.

Other Indian candidates used newer methods. The portal records them at trial stage.

What are the key facts?

• Gennova’s HGCO19 was called the nation’s first mRNA-based COVID-19 vaccine.
• Its interim phase I data were found safe, tolerable and immunogenic. The DCGI office then approved a phase II and III study.
• Bharat Biotech’s BBV154 is an intranasal vaccine. It uses a replication-deficient chimpanzee adenovirus vector.
• It was the first nasal vaccine to get regulator approval for phase 2 trials in India.
• Dr Reddy’s worked on the Russian vaccine Sputnik V in India. The PIB briefing lists Sputnik V as a viral vector vaccine.

What is the memory hook?

Think “Gennova mRNA, Bharat nasal, Reddy’s Sputnik”.

Vaccines protect the person and also the people around them.

What are the key facts?

• Some people cannot take certain vaccines. They include people with weak immune systems or severe allergies.
• They can still be safe if the people around them are vaccinated.
• When many people in a community are vaccinated, the germ has a hard time spreading.
• India’s COVID-19 vaccination drive began on 16 January 2021.
• Health workers were one of the first priority groups.
• The CoWIN platform let citizens book vaccination appointments.

What is the memory hook?

Think “many immune people, few places to spread”.

CDS asked about vaccine types. UPSC Mains asked about the principle and the Indian approaches.

What were the questions?

What are the answers?

• CDS-I 2022: option (c). Covishield is also viral vector-based, not mRNA.
• UPSC Mains 2022: explain the principle, then the mechanism, then each platform. Name Covaxin, Covishield, ZyCoV-D and Corbevax.

What are the traps?

• Covishield is a viral vector vaccine, not mRNA.
• Covaxin kills the whole virus. It is not a vector vaccine.
• ZyCoV-D is DNA-based and has three doses. Corbevax is protein sub-unit and has two doses.
• Do not call HGCO19 or BBV154 approved vaccines. This lesson records only their trial approvals.

What is the memory hook?

Think “shield carries, vaxin kills”.