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Vaccines in General and Specific for COVID-19.

Updated: Jan 8, 2021

To understand how COVID-19 vaccines work- we should first understand how our bodies fight illness. When germs, such as the virus (SARS-CoV-2) enter our bodies they attack and multiply. This attack is called infection, which causes us to fall ill.

Our immune system (body's defense system) uses several tools to fight infection. There are two main components of the immune system.

  1. Cellular Immunity

  2. Antibodies

Antibodies are protein molecules secreted by immune cells, having a very specific shape. This shape is complementary to the virus and therefore, tightly binds to the virus and does not allow the virus to enter into new cells.

However, the process of antibodies generation by our immune system takes some time. This delay may lead to severe infection and the person needs to be hospitalised. To overcome this limitation, we are given a vaccine. Vaccine is none other than the same virus ( killed whole Virus) or part of the virus cells which are injected in our body. Our immune system does not differentiate between live/dead virus or part of a virus and therefore, start producing antibodies.

Fact 1: As the vaccine does not have live virus we will not get infection but our body produces antibodies. These antibodies protect us from future infection with the same virus (let's say SARS-CoV- 2)

In conclusion, vaccination is the process by which we prepare (or train) our body to fight against future infection.


Different types of vaccines for COVID-19

Currently, there are three main types of COVID-19 vaccines that are or soon will be available for mass vaccination. The difference in each type of vaccine is how they prompt our bodies to recognize (i.e. the way it trains our body to fight against coronavirus) and protect us from SARS-CoV-2.

Source - Nature

  • mRNA vaccines (made by Pfizer, BioNTech, MODERNA) contain pieces of genetic material from the virus that causes COVID-19. Once this piece is delivered to our body, it produces that particular protein (spike protein of SARS-CoV-2 - responsible for infection). Our body recognizes this protein and starts producing antibodies against this spike protein. m-RNA being an unstable molecule it will get disintegrated in our body and shall get eliminated. Our body has genetic material in the form of DNA while the proposed vaccine is RNA and therefore, there is no danger from it in altering our genetic material.

  • Protein subunit vaccines (made by Sanofi and GSK) contain harmless pieces (proteins) of SARS-CoV-2 that cause COVID-19. Here small protein (mainly spike protein) is used to train our body. Once vaccinated, our immune system recognizes the proteins that don’t belong to our body and begins making fighter cells (T-lymphocytes and antibodies). If we are ever infected in the future, memory cells will recognize and fight the virus.

  • Vector vaccines (made by AstraZeneca- Oxford, Sputnik- V) contains a weakened or non-infectious virus other than SARS-CoV-2. For example AstraZeneca uses Chimpanzee adenovirus while Sputnik-V uses human adenovirus. These viruses are inserted with genetic material obtained from SARS-CoV-2 and therefore, produces the same spike protein like SARS-CoV-2. Once entered into the body, our immune system recognises these spike proteins and starts producing antibodies. If we are ever infected in the future, these antibodies will recognize and fight the virus.

  • Attenuated or killed virus (made by Bharat Biotech) vaccines use the SARS-CoV-2 but in either killed or weakened form. This whole virus is injected in our body to generate immunity. Most of the current vaccines including the Polio and the Flu shots we take each year are based on this technology.


Stages of Vaccine Trials

  1. Animal studies.

  2. Phase 1 clinical trial ( limited number of human volunteers).

  3. Phase 2 clinical trial (medium size population) and Phase 3 clinical trial with more than 20,000 volunteers.

Stage 1 and 2 determine the safety and immunogenicity while the stage 3 determines the efficacy data. Phase 3 trial is a double blind, randomized trial where the volunteer