Phases of Clinical Trials

Clinical Trials
A Phase I trial is the first setting in which an experimental HIV vaccine is given to people. The trial, which can last up to 2 years, may enroll between 20 to 100 HIV-uninfected volunteers at low risk for HIV infection.

A Phase I trial primarily seeks information on safety, particularly looking for any vaccine-related side effects. The trial can also provide data on the dose and administration schedule needed to achieve the optimal immune responses.

If the vaccine elicits neutralizing antibodies or cytotoxic T lymphocytes (CTLs), scientists can study whether these responses are broadly protective against a wide variety of HIV strains that scientists refer to as subtypes or clades.

Once Phase I trials show the experimental HIV vaccine is safe, well tolerated, and appears promising, it can advance into Phase II. These trials, which can last longer than 2 years, enroll between 100 to 300 volunteers at high and low risk for acquiring HIV.
In these trials researchers gather more data on safety and immunogenicity.

Investigators supported by the National Institute of Allergy and Infectious Diseases (NIAID) investigators are also developing designs for intermediate trials that can provide preliminary answers about a candidate vaccine's efficacy, and determine if the vaccine candidate should move forward into large Phase III, or efficacy, trials.

A Phase IIb trial, also known as a "proof-of-concept" trial, is smaller, requiring 2,000 to 5,000 volunteers, is less expensive than Phase III trials, and may provide clues about the immune responses that can protect against disease.

The most promising vaccine candidates move into Phase III, enrolling 10,000 or more HIV-uninfected people at high risk for exposure to the virus. A Phase III trial, which can last up to 4 years, is typically designed to ensure enough data are collected on safety and effectiveness to support a license application to FDA.