ChAdOx1

Subject: Science and tech

Context:

According to Lancet journal, avaccine AZD1222 developed at the University of Oxford has shown encouraging results in early human testing and appears to be “safe well-tolerated, and immunogenic”.

Concept:

• The AZD1222 vaccine is based on a chimpanzee adenovirus called ChAdOx1 which elicited antibody and T-cell immune responses in human body.
• It is made from a genetically engineered virus that causes the common cold in chimpanzees. However, the virus has been modified so that it doesn’t cause infection in people and also to mimic the coronavirus.
• The vaccine is already undergoing combined Phase II/III trials in the UK, Brazil and South Africa.

Working Mechanism

• The vaccine belongs to a category called non-replicating viral vector vaccines which tries to build the body’s immunity against spike proteins (allow the virus to penetrate cells and, thereafter, multiply).
• The idea is to create antibodies to fight this spiked surface so that the virus does not even have the chance to penetrate the cells.
• The adenovirus, genetically modified so that it cannot replicate in humans, will enter the cell and release the code to make only the spike protein. The body’s immune system is expected to recognise the spike protein as a potentially harmful foreign substance, and starts building antibodies against it.
• Once immunity is built, the antibodies will attack the real virus if it tries to infect the body.

Vaccine types:

• Inactivated: It is made using particles of the Covid-19 virus that were killed, making them unable to infect or replicate. Injecting particular doses of these particles serves to build immunity by helping the body create antibodies against the dead virus.
• Non-replicating viral vector: It uses a weakened, genetically modified version of a different virus to carry the Covid-19 spike protein.
• Protein subunit: This vaccine uses a part of the virus to build an immune response in a targeted fashion. In this case, the part of the virus being targeted would be the spike protein.
• RNA: Such vaccines use the messenger RNA (mRNA) molecules that tell cells what proteins to build. The mRNA, in this case, is coded to tell the cells to recreate the spike protein. Once it is injected, the cells will use the mRNA’s instructions, creating copies of the spike protein, which in turn is expected to prompt the immune cells to create antibodies to fight it.
• DNA: These vaccines use genetically engineered DNA molecules that, again, are coded with the antigen against which the immune response is to be built.