Herd immunity has been a goal of many governments in the COVID-19 pandemic, but methods have been different depending on different factors of the country.  

Herd immunity against SARS-CoV-2 virus

- herd immunity against the SARS-CoV-2 virus

Michigan State University

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

Development of COVID-19 Vaccines

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. 

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