Phase I is an initial trial with a small group of healthy volunteers and usually takes a few months.
Phase II examines consistency of the vaccine, any potential side effects and the presence of the expected immune response. This phase can last several months.
Phase III gathers robust data on safety and efficacy and can last several years as it usually involves thousands of volunteers.
Phase IV occurs after the vaccine is licenced and used in the public. This phase continues for as long as the vaccine is being used in the community and monitors the vaccine’s benefits and any side-effects.
