Vaccines for COVID-19 - Broad Learnings

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More than a hundred different teams of scientists are developing vaccines for COVID-19. Developing vaccines from scratch is not the fastest option for stopping the ongoing pandemic no matter how effective they will be, but it is does constitute the desirable long-term solution.

The time required to develop and deploy a safe and effective vaccine is typically 10-15 years (Figure 1). However, for COVID-19, the attempt is to compress to over a year.

Vaccine development requires extensive planning regarding the following:

vaccine design
vaccine production and purification
pre-clinical testing in animals (to ensure some safety in humans)
multiple phases of clinical trials in humans (phase 1 for safety as well as phases 2 and 3 for efficacy).

Figure 1. Traditional timeline of vaccine development (image courtesy https://www.gao.gov/products/GAO-20-583SP)

Vaccines aim to expose the body to an antigen that does not cause disease but provokes an immune response that can block or kill the virus if a person becomes infected.

Various strategies used for vaccine development are live attenuated or inactivated viruses, virus-like particles or other protein-based approaches, viral vector–based vaccines or nucleic acid–based vaccines.

These vaccines mostly target the spike proteins covering the surface of the virus and helping virus to invade the human cell.

This course covers types of vaccines and strategies being used to create vaccines to fight COVID-19.

Types of Vaccines

Whole virus vaccine

It is also known as Inactivated and Live inactivated vaccines. Weakened or live vaccines are attenuated form of the germ that causes a disease.

Inactivated vaccines use the killed version of the germ that causes a disease. However, they tend to provide a shorter length of protection than live vaccines, and require boosters to create long-term immunity.

DNA vaccine

A DNA vaccine against a microbe evokes a strong antibody response to the free-floating antigen secreted by cells.

The vaccine also stimulate a strong immune response against the microbial antigens displayed on cell surfaces. It is an inexpensive vaccine.

Figure 2. Process of making of DNA vaccine

Source: NIAID Begins Clinical Trial of West Nile Virus Vaccine

RNA vaccine

Vaccine based on delivering messenger RNA into cells instead of DNA. The cells read the mRNA and are translated into proteins that elicit protective immunity against the infectious agent.

Viral vector vaccine

Vaccine that use a virus to deliver coronavirus genes into cells. There are two types:

those that can still replicate within cells (replicating)
those that cannot (non- replicating) because key genes have been disabled.

Protein-based vaccine

This is composed of purified or recombinant proteinaceous antigens from a pathogen, such as a bacterium or virus.

When administered in the body, a protective immune response occurs against the pathogen.

Recombinant vaccine

It is produced through recombinant DNA technology. Yeast or other cells can be engineered to carry a virus’s gene.

	Whole virus vaccine	DNA vaccine	RNA vaccine	Viral vector vaccine	Protein-based vaccine	Recombinant vaccine
Definition	Modifies entire virus to provoke immune response	Uses part of genetic code of coronavirus	Based on delivering mRNA into cells	Use of virus to deliver coronavirus genes to cells.	Uses coronavirus protein	Produced through recombinant DNA technology
Other names	Inactivated and Live attenuated Vaccines	Genetic vaccine	RNA vaccine	Adenovirus vector vaccine	Virus-Like Particle vaccines	Recombinant Vector vaccine
Conventional examples of vaccine	Influenza, chickenpox, MMR	Canine melanoma Humans: None	Under clinical trials for MERS and a few other diseases	H.I.V. & Ebola	HPV	Shingles and Hepatitis B