MEDICINE FOR ALL

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

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

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

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

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

VIRUS VACCINES

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

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