TA Explained: How COVID-19 vaccines work?

By Dr. Haryax Pathak

Let’s talk about vaccines. I am still seeing a lot of confusion going around about the mechanism of vaccines in use. In this explainer, I attempt to explain the functioning of various vaccines in use, as simply as possible.

What is the virus made of?

So, think of the SARS-CoV-2 virus as Ferrero Rocher for the purpose of very simple understanding.

  • Spike Protein = Nutty spikes
  • Lipid Membrane = Outer Chocolate Layer
  • Nucleocapsid = Wafery Layer
  • RNA = Innermost Chocolate

How does virus causes an infection?

The virus enters through our respiratory tract. It needs to enter a cell to replicate. For that, it uses the Spike Protein (nutty spikes). Spike protein allows the virus to enter the cell and cause infection.

What does vaccines do?

The aim of vaccines is to try and prevent infection in your body. Hence, most of the vaccines are targeting the Spike Protein. Scientists sequenced the RNA (innermost chocolate) of the virus and identified the genes making the Spike Protein.

Let’s see some vaccines now.


Imagine if someone took away all taste and flavour of Ferrero Rocher. It is now lifeless, tasteless. That’s Covaxin (by Bharat Biotech). They killed the SARS-CoV-2 virus, took away its ability to cause infection. Though the human Body can still identify it and mount an immune response against it. It is the only vaccine in application right now that uses an inactivated virus. All the other vaccines (we’ll see below) – target only the Spike Protein (nutty spikes).

Covishield , Sputnik V and Janssen

What if I use the crunchy nuts of Ferrero in another chocolate? Maybe Snickers? That’s Covishield (by Oxford University and AstraZeneca). The genes making the Spike protein are mixed into an adenovirus (a group of common viruses – flu, cold, cough etc.) that can’t cause infection in humans. It makes the Spike Protein in our body.

The vaccines Sputnik V (by Gamaleya Research Institute) and Janssen (by Johnson & Johnson) are similar to Covishield.

Covishield uses a Chimpanzee adenovirus. Sputnik V and Janssen use a Human adenovirus. The mechanism is the same – adenovirus is used as a vehicle to send the spike protein gene to our body.

Pfizer, Moderna and ZyCOVD

What if I can somehow teach my own body to make those crunchy Ferrero nuts? That’s mRNA (messenger RNA) vaccines – Pfizer and Moderna. The genes making Spike Protein are encoded into an mRNA. mRNA further makes the Spike Protein in our body.

A similar mechanism is also used by ZyCoVD vaccine (by Zydus Cadila). Instead of mRNA, ZyCoVD uses plasmid DNA (a free-floating piece of DNA) that contains the code for the Spike Protein. ZyCoVD is still undergoing trials in India.


What if I just want to eat the ready-made nuts of Ferrero? That’s Covovax (by Novovax). They took the code for the Spike Protein, put it into another virus called baculovirus and allowed it to infect moth cells. The infected cells produced spike proteins that spontaneously joined together to form spikes, as they do on the surface of the coronavirus. Spike proteins made were collected, made into nanoparticles, and used as vaccine.

In the simplest of words – they made the spike protein outside the body, in a lab – and then inject it as a vaccine.

Covovax is the brand name of the vaccine developed by Novavax, USA, and manufactured in India by Serum Institute – undergoing bridging trials in India.

Can these vaccine cause any kind of infection?

So, as you can see from above – none of the vaccines have a complete, living virus that can cause infection.

Covaxin has the killed virus – unable to cause infection. All others – barely have 1 component of the virus – the Spike Protein.


So, all in all, this is how the vaccines in use/undergoing trials work. They are safe. They are efficacious. Get vaccinated when you can. And, implore others to get vaccinated as well.

(Author is a doctor from Vadodra. He specializes in Health Communication, Public Health, and Health Policy. Dr. Pathak tweets at @HaryaxPathak)

Featured image source: HaryaxPathak/Twitter

The Analysis (TA) is a research and communication group | Analyzing India’s legal, policy and political affairs. Write to us at contact@theanalysis.org.in

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