- Pfizer-BioNTech COVID-19 vaccine is an mRNA vaccine. It uses messenger RNA to instruct cells to make a spike protein that triggers an immune response. (A-3) - Covaxin, developed by Bharat Biotech, is an inactivated vaccine. It contains whole virus particles that have been chemically inactivated so they cannot cause disease but can still trigger an immune response. (B-2) - Sputnik-V, developed by the Gamaleya Research Institute, is an adenovirus- based vector vaccine. It uses modified adenoviruses (harmless cold viruses) to deliver genetic instructions for the spike protein. (C-4) - ZyCoV-D, developed by Zydus Cadila, is a plasmid DNA vaccine. It uses a circular piece of DNA called a plasmid to deliver genetic material encoding the spike protein. (D-1)