COVID-19 vaccine development part 16

Why there are so many COVID-19 vaccines in development :

  • There are many different COVID-19 vaccines in development because it is not yet known which ones will be effective and safe
  • Based on experience, roughly 7% of vaccines in preclinical studies succed. Candidates that reach clinical trials have about a 20% chance of succeeding
  • Different vaccine types may be needed for different population groups
  • For example, some vaccines may work in older persons and some may not, as the immune system weakens with older age
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COVID-19 vaccine development part 15

Steps in vaccine development :

(Action taken to ensure a new vaccine is safe and works well)

  • Pre-clinical studies

      Vaccine is tested in animal studies for efficacy and safety, including challenge studies

  • Phase I clinical trial

      Small groups of healthy adult volunteers to receive the vaccine to test for safety

  • Phase II clinical trial

      Vaccine is given to people who have characteristics (such as age and physical health) similar to those for whom the new vaccine is intended

  • Phase III clinical trial

      Vaccine is given to thousands of people  and tested for efficacy and safety

  • Phase IV post marketing surveillance

      Ongoing studies after the vaccine is approved and licensed, to monitor adverse events and to study long-term effects of the vaccine in the population

  • Human challenge studies

      Study in which a vaccine is given followed by the pathogen against which the vaccine is designed to protect. Such as trials are uncommon in people as they present considerable ethical challenge

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COVID-19 vaccine development part 14

Nucleic acid vaccines :

  • Instead of a virus, a protein antigen, or a virus expressing the protein, nucleic acid coding for the antigen is injected
  • DNA plasmid: enters nucleus, translated to mRNA for expression of protein
  • Or  mRNA can be injected. More direct (no translation required) but less stable than DNA
  • This is new technology – no other vaccines for human use have used this
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COVID-19 vaccine development part 13

Viral vector vaccines :

  • The gene for a pathogen protein is inserted into a different virus that can infect someone without causing disease
  • The safe virus serves as a “platform” or “vector” to deliver the protein that triggers an immune response
  • The safe virus is then injected as a vaccine
  • Some replicate (reproduce) in the body and some do not
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COVID-19 vaccine development part 12

Protein-based vaccines :

  • A protein is extracted from the virus (alive or inactivated), purified, and injected as a vaccine
  • For coronavirus, this is most commonly the spike protein
  • Virus-like particles work in the same way

 

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COVID-19 vaccine development part 11

VIRUS VACCINES

Virus is selected, modified (weakened) or completely inactivated so that it will not cause disease

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COVID-19 vaccine development part 10

Immunogens used to develop viral vaccines :

Nucleic acids :

  • DNA or RNA coding for a viral protein
  • Strong cellular immunity, rapid development
  • Relatively low antibody response
  • Example of vaccines
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COVID-19 vaccine development part 9

Immunogens used to develop viral vaccines :

Replicating or non-replicating viral vector :

  • Viral pathogen expressed on a safe virus that doesn’t cause  disease
  • Rapid development
  • Prior exposure to vector virus (eg. adenovirus) may reduce immunogenicity
  • Example of vaccines : Ebola

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COVID-19 vaccine development part 8

Immunogens used to develop viral vaccines

Peptides :

  • Synthetic produced fragment of an antigen
  • Rapid development
  • Poorly immunogenic; high cost
  • Example of vaccines : COVID-19 vaccines in development
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COVID-19 vaccine development part 7

Immunogens used to develop viral vaccines :

Recombinant :

  • Host cell is used to express an antigen
  • No need to produce the whole virus
  • May be  poorly immunogenic; high cost
  • Example of vaccines : Hepatitis B
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