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
