TABLE 1.

Phases of Clinical Evaluation of an Investigational Vaccine

Phase Number and Type of Study Participants	Scientific 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?

Source. Adapted from: Centers for Disease Control and Prevention: Vaccines. Parents. CDC.gov website. https://www.cdc.gov/vaccines/parents/infographics/journey-of-child-vaccine-h.pdf. Updated July 2018. Accessed December 12, 2020.