Covishield (ChAdOx1 nCoV- 19 Corona Virus Vaccine) is one the vaccine developed against Covid-19 caused SARS-Cov-2, it is Oxford-AstraZeneca vaccine manufactured in India by Serum Institute. It is a recombinant vaccine.
Recombinant vaccine is produced using recombinant DNA technology, it involves insertion of DNA that codes for antigen stimulating immune response into a harmless viral/bacterial vectors.
Covishield vaccine contain gene coding SARS-Cov-19 S spike protein in to adenovirus which is modified version of a chimpanzee adenovirus (ChAdOx1), enters into the cell but doesn’t replicate inside it.
After administration of vaccine to the Intramuscular region of the arm, the adenovirus carrying the gene of spike protein enters into the cell by endosomes, thereby releasing the gene into the nucleus. In the nucleus the gene is transcribed into mRNA and this mRNA will leave out of the nucleus, enters into cytoplasm for protein synthesis by ribosome machinery. The synthesized spike proteins migrate to the cell surface by endosome and release the spike proteins outside the cell. These proteins are recognized by Antigen-presenting cell (APC). APC processes the spike proteins and present it to CD4+ T cells, this CD4+ T cells stimulate the Th2 cytokines which send signals for the differentiation of B cells by “Clonal Proliferation” and produce Antibodies specific to the virus. Some of the B cells differentiate into plasma cells and produce antibodies as initial primary response and some other B cells will differentiate into memory B Cells which remain as stock storage and stimulate antibodies production up on future infections. The produced antibodies will neutralize and opsonize the viral particle thus no severe damage will be caused.
Fig . Schematic representation of mechanism of vaccine. 1. The injected virus entering into the cell. 2. The virus is packed in endosome and direct it to the nuclear membrane. 3. Only the DNA coding Spike protein entering into the nucleus and transcription occurs, the transcribed mRNA leaves nucleus and enter into cytoplasm. 4. The mRNA is translated into proteins by Ribosome machinery and synthesize the spike protein S of SARS-Cov-19. 5. Spike protein migrates to the surface of cell.
