Covid 19 Vaccines
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- Vaccine science is crucial for effective decision making. For COVID-19, there are questions about different vaccines and platforms, their advantages, disadvantages, safety and efficacy.
Various Types of Vaccine:
- Inactivated Viruses:
- COVAXIN developed by Bharat Biotech
- mRNA Vaccines
- mRNA 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 body’s cells to recreate the spike protein of the coronavirus SARS-CoV-2. It is the spike protein which appears as spikes on the surface of the coronavirus – that initiates the process of infection. They prompt the immune cells to create antibodies to fight it.
- Conjugate Vaccine for COVID-19
- Basics of Conjugate Vaccines:
- A conjugate vaccine is a type of subunit vaccine which combines a weak antigen with a strong antigen as a carrier so that the immune system has a stronger response to the weak antigen.
- Soberana 02, a conjugate COVID-19 vaccine developed in Cuba, was given emergency use authorization in Cuba and Iran.
- Cuba’s state run corporation, BioFarma, said that it has indigenously produced Soberana 2 vaccine which has 2% efficacy in phase-3 trials.
- In Soberana 02, the spike protein is linked to tetanus toxoid, making it a conjugate vaccine.
- Basics of Conjugate Vaccines:
- It provides more effective response
- For an effective response, not only antibodies but even killer T-cells, or those produced by the immune system and capable of destroying infected cells, must be produced.
- Spike protein may be able to elicit a strong vaccine response but when combined with tetanus toxoid, such a T-cell response could also be generated which can confer more effective protection:
- Note: Tetanus Toxoid is a very widely used childhood vaccine and therefore one which immune system recognizes.
- The design and manufacturing allow the vaccine to be stored in regular refrigerator settings of 2-8 degree Celsius.
- Note: Soberana 02, is by far (July 2021) the only one among coronavirus vaccine candidates that relies on the conjugate vaccine technology.
- Adenovirus Route
- In this method, the adenoviruses (common cold virus) are weakened so that they don’t replicate in humans. They are also modified to make the code for coronavirus spike protein. Spike proteins help the body recognize it and make antibodies against the spike protein. These antibodies will help mount an immune response and prevent the virus from entering the human cells and cause an infection.
- Oxford-AstraZeneca (ChAdOx1 nCoV-19), are using the Adenovirus route.
- Covishield used in India is a version of this.
- Sputnik V Vaccine also has gone Adenovirus route
- It uses two different viruses that cause common cold (adenovirus) in humans. The viruses are weakened so they can’t replicate in humans and cannot cause disease. They are also modified to make the code for coronavirus spike protein.
- DNA Vaccines
- E.g. INO-4800 by Inovio (a US pharma company)
- the DNA vaccine injects a part of genetic code of the virus (spike protein), which allows cells to produce antigens – a molecule present on the outer surface of the virus. This triggers immune responses.