Last week, India’s pharmaceutical major Zydus Cadila sought ‘emergency use authorisation’ for its invention ‘plasmid DNA vaccine’, which it calls ‘ZyCoV-D’.

A plasmid is a type of DNA that is found only in bacterial cells. They are distinct from the chromosomal DNA. When people mention ‘DNA’ they normally refer to the chromosomal DNA — the old, familiar double-helix ladder. The plasmid DNA, unlike the chromosomal DNA, does not carry hereditary information, but its genes give it advantages such as pesticide- and antibiotic-resistance.

Scientists have used plasmid DNAs as a vector, or ‘trucks’, to carry other materials into cells.

A plasmid DNA vaccine works like this: A piece of DNA encoding the antigen (part of the disease-causing pathogen that induces an immunity response from our bodies) is inserted into a bacterial plasmid. The DNA plasmids carrying the antigen are injected into the muscle. Once the DNA gets inside our cells, they start producing antigens, which triggers an immune response.

The advantages are that (like the mRNA vaccines) the plasmid DNA vaccines can be easily manufactured, are inexpensive and safer.

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