Sunday Story
Vaccine Talk
Writer: Aparna Sundaresan



Bad news—the disease Covid-19 and the coronavirus that causes it haven’t gone anywhere. Good news—there are now vaccines available to help us defend against the virus and the illness. One of the Covid vaccines available in India is called Covishield, developed by Oxford University in the UK and European pharmaceutical company AstraZeneca.

But how does it work?

So, we know that Covid-19 is caused by a coronavirus called SARS-CoV-2.
The surface of the SARS-CoV-2 virus has several proteins which allow the virus to enter our cells and cause infection. These proteins are laid out as spikes on the virus’ surface and are called spike proteins.

Credit: torstensimon/

Viruses have always been good at getting into cells. So, research has been ongoing for some time now on how to use the viruses themselves to combat other viruses. A lot of research has been focused especially on the adenovirus. This virus causes colds and flu-like symptoms. The Covishield vaccine uses chimpanzee adenovirus (it causes infection in chimpanzees) but with a slight modification—this adenovirus can enter human cells, but can’t reproduce inside our cells and cause their own infection.

The adenovirus in the vaccine has also been modified to carry instructions on how to make the spike proteins that the SARS-CoV-2 virus has. The instructions are in the form of DNA. DNA is a material that is present in nearly every living being and carries instructions on how to grow and develop.

Once the adenovirus enters our cells, it releases the DNA it is carrying. The instructions on the DNA are read by our cells and copied into a molecule called messenger RNA or mRNA. The mRNA then reads the instructions and starts building spike proteins, as well as fragments of spike proteins, on the surface of our cells. 

When this happens, our immune system is activated. The immune system recognizes the spike proteins built on our cells and becomes prepared to fight them. Cells in our immune system start creating antibodies—substances that fight bacteria, viruses and other foreign invaders in our body. These antibodies learn to attach themselves to the SAR-CoV-2 spike proteins, block them from entering our cells and then destroy them. Now when the actual virus enters our body, our immune system already knows how to identify and destroy them. 

The Covishield vaccine is given in two doses to better prepare our immune system. Around two weeks after getting each dose, our immune system is primed to fight the virus.

On the other side of the world in the USA and UK, people are being given the Pfizer-BioNTech vaccine. It works a bit differently. Instead of using an adenovirus, the mRNA with instructions on how to make the spike proteins is wrapped inside bubbles of fat and injected into the body. The mRNA enters our cells and then works the same way as the Covishield vaccine.

Hindustan Times
New York Times
New York Times Interactive
American Council on Science and Health
New York Times Interactive
US Centre for Disease Control and Prevention
Smithsonian Magazine
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