Vaccine development comes with a host of problems that slows down the progression of producing one. Aside from the economic and time-sensitive factors, vaccines come with alternative effects that need to be studied and approved by national organizations (FDA) for general use:
- Antibody-dependent-enhancement (ADE)
- Comorbidities 
- Challenge studies

Challenges to vaccine development

The majority of COVID-19 vaccine candidates target the spike protein and receptor-binding domain of the virus. This is because the spike protein binds to the ACE2 receptor on the surface of host cells.
Other structural antigens targeted are the envelope, membrane, and nucleocapsid proteins of the virus with studies identifying B and T epitopes being done currently.

Vaccine antigen selection and design

A viable vaccine should provide the host long-lasting immunity without side-effects by neutralizing the S protein of the virus through a balanced T-cell and antibody immunologic response. 
The goal is to avoid the current immunologic response of producing a cytokine storm without encountering ADE specific challenges.

Protective Immunity

- Transitioning from animal testing to human clinical trials
- The resources needed to produce a vaccine
- The duration and magnitude of the immunity provided by a potential vaccine

Preclinical evaluation of vaccine efficacies and safety

- manufacturer engagement in developing vaccine
- regulating organizations
- cold chain
- various production platforms

Factors involved in Manufacturing

It might not take until 2024 to get a full safe vaccine for COVID-19. There may not be enough to treat everybody since two rounds are going to be needed to gain full immunity. The two rounds of the vaccine will be given a month apart. The FDA is hoping to come out with a vaccine by October to have as a temporary one. 

Global Distribution 

- herd immunity against the SARS-CoV-2 virus

Goals of COVID-19 vaccine development

Includes the scientific challenges and direction the development of COVID-19 vaccines.
- Challenges of development
- Vaccine antigen selection and design 
- Protective immunity 
- Preclinical evaluation of safety
- Manufacturing 
- Vaccine design itself is complicated
- Need for cold chain
- Consideration of cost
- Global distribution
-Authorization by US Food and Drug Administration and VRBAC
- Goals of development

Carnegie Mellon University

Stanford University

San Jose State University

University of California, Santa Cruz

University of Michigan - Ann Arbor

Bowdoin College

- Development of COVID-19 Vaccines
- Types of Vaccines:
     - Virus Vaccines
     - Nucleic Acid Vaccines
     - Viral Vector Vaccines
     - Subunit Vaccines

Genetic Engineering in Vaccine Development for COVID-19

Chen, W. (2020). Promise and challenges in the development of COVID-19 vaccines. Human Vaccines & Immunotherapeutics, 1-5. doi:10.1080/21645515.2020.1787067

Promise and challenges in the development of COVID-19 vaccines

Nucleic Acid Vaccines use genetic material (DNA/RNA) from a viral protein that induces an immune response. The nucleic acid is inserted into human cells, which create copies of the virus protein. For many COVID-19 vaccines in development, the nucleic acid codes for the virus's spike protein. Both DNA and RNA vaccines trigger CD8+ cytotoxic T cell response to eradicate virus, in addition to antibody and CD4+ T cell responses.
However, because of their remarkable risk of failure, not a single nucleic acid vaccine has ever been licensed.

Some types of nucleic acid vaccines include (image):

Nucleic Acid Vaccines for COVID-19

Viral-Vector vaccines genetically engineer another virus, referred to as vectors, to carry genetic materials from the coronavirus and produce coronavirus proteins in the human body. These vectors are weakened and does not cause disease. Two main types are (shown in image):

Viral-Vector Vaccines for COVID-19

Virus vaccines use the virus itself, or  in a weakened or inactive form.

Virus Vaccines for COVID-19

Recent efforts to find a possible working vaccine for COVID-19 has allowed vaccine development to be distinct from traditional vaccines. Traditional vaccines for most viruses are either virus-based or protein-based. The idea behind next-generation vaccine platforms is to be able to develop a vaccine based on only sequence information and not by culturing the virus. Some of the non-traditional vaccines currently being developed are viral vector, nucleic acid-based vaccines and antigen-presenting cells.

New methods for COVID -19 vaccine development

Development of COVID-19 Vaccines

Nanotechnology is used to create modern vaccines because nanomaterials are best for antigen delivery. Nanotechnology advances have helped novel vaccine candidates to clinical trials at a surprising speed. Nanotechnology and viruses work at the same length scale, which specifically helps vaccine development. mRNA vaccine being developed is delivered through lipid nanoparticles.

Nanotechnology in vaccine delivery

Subunit vaccines use only the essential antigen or other purified protein subunits of the pathogen via a harmless vector that can best stimulate the immune system. The chance of developing an adverse reaction is significantly lower than in other vaccine types and they elicit a strong immune response. However, they often require adjuvants to stimulate an adequate response and it is difficult to identify the precise antigens that induce long-term immunity.

Subunit Vaccine

- NVX-CoV2373 from Novavax Inc
- Anhui Zhifei Longcom / Chinese Academy Vaccine
- CoVLP from Medicago
- rAd26-S and rAd5-S (Sputnik V) from the Gamaleya Center 
- Ad26.COV2.S from Johnson & Johnson
- Ad5-nCoV from CanSino Biologics
- ChAdOx1 nCoV-19 from The University of Oxford
- mRNA-1273 from ModernaTX
- BNT162b2 from Pfizer and BioNTech
- Bacillus Calmette-Guerin (BCG) Vaccine from Murdoch Institute in Australia
- Vaccine from Wuhan Institute of Biological Products Vaccine
- CoronaVac from Sinovac Biotech Ltd
- BBIBP-CorV from Beijing Institute of Biological Products
- BBV152 from Covaxin



Vaccine Candidates of Interest (Lit Review)

• DNA vaccine consists of delivering genes or fragments of it, encoding immunogenic antigens to the host's cells by using DNA plasmids as a vector.

• Compared with traditional live or attenuated vaccines, DNA vaccines have several advantages, such as induction of broad immune responses without any risk being associated with replicating microorganisms; stimulation of both cellular and humoral immunity; construction of a vector encoding different antigens in a single vaccine; efficient large-scale, low-cost, production; and high storage stability

• A clinical trial was designed to evaluate the safety and tolerability of orally immunized bacTRL-Spike vaccine in healthy adults. However, this study has not yet started recruiting, and the estimated completion date is December 31, 2021 Moreover, the safety and immunogenicity of GX-19, another DNA vaccine against COVID-19 that uses intramuscular immunizations are already in clinical trials.

• mRNA vaccines do not need to reach the cell nucleus like the DNA ones, which is one of the potential practical advantages. The mRNA-1273 (Moderna Inc. Cambridge, MA, USA) was the first mRNA vaccine to be designed against COVID-19 and has achieved a time record of 63 days from vaccine design to human trials.

• Developing vaccines against COVID-19 require further studies on gene mutations and how to avoid vaccine failure because of them.

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