Phases of Clinical Evaluation of an Investigational Vaccine

Phase Number and Type of Study ParticipantsScientific Questions Asked
1 20 to 100 healthy adults
  • Is the vaccine safe?

  • Is the vaccine tolerable?

  • What are the vaccine side effects in relation to the dose administered?

  • Does the vaccine cause the desired immune response?

2 Several hundred from target population
  • What is the desired vaccine dose and dosing interval?

  • Is the desired immune response to the vaccine achieved?

  • What are the common short-term vaccine side effects observed?

3 Several hundred to tens of thousands from target population
  • How effective and safe is the vaccine when comparing people who receive the vaccine to people who do not receive the vaccine?

  • What are the most common side effects?

  • Is the safety and immune response in study participants consistent across different lots of vaccine manufactures?

  • What is the effect on safety and immune response when the vaccine is co-administered with other vaccines?