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  • Recently, Moderna announced results of human trials on the vaccine it has developed with US National Institutes of Health. The trials found the vaccine 94.5 per cent effective, and the announcement comes days after Pfizer had released trial results showing 90 per cent effectiveness in its own vaccine, developed in collaboration with BioNTech-Fosun Pharma.
  • The Moderna and Pfizer vaccines use the same technology, based on messenger RNA, or mRNA. Such vaccines make use of the messenger RNA molecules that tell the body’s cells what proteins to build.
  • The mRNA, in this case, is coded to tell the cells to recreate the spike protein of the coronavirus SARS-CoV-2, which causes Covid-19. It is the spike protein — which appears as spikes on the surface of the coronavirus — that initiates the process of infection; it allows the virus to penetrate cells, after which it goes on to replicate. 
  • A coronavirus vaccine based on mRNA, once injected into the body, will instruct the body’s cells to create copies of the spike protein. In turn, this is expected to prompt the immune cells to create antibodies to fight it.
  • These antibodies will remain in the blood and fight the real virus if and when it infects the human body.
  • Other types of vaccine include the non-replicating viral vector category, an example of which is the vaccine developed by Oxford and AstraZeneca.

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  • The vaccine uses a different virus — in the Oxford-AstraZeneca case, a weakened version of a common cold virus (adenovirus) that infects chimpanzees — to carry just the code to make the spike protein, like a Trojan horse.
  • The adenovirus, which has been 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.
  • Then there are inactivated virus vaccines made by using particles of the Covid-19 virus that were killed, making them unable to infect or replicate; protein subunit vaccines that use a part of the virus (spike protein again, in this case) to build a targeted immune response towards; and DNA vaccines that use genetically engineered DNA molecules that, again, are coded with the antigen against which the immune response is to be built.