How are new vaccines tested before public use?
It is reasonable to ask how new vaccines are tested before they are cleared for public use. The National Institute of Allergy and Infectious Diseases explains the various studies that must be done before the new vaccine is approved by the FDA. There are various stages of testing a vaccine must undergo before it is cleared for use. They are as follows.
1) Animal Testing – Firstly, the new vaccine is tested in animals for safety and immunogenicity, meaning that is must be safe and induce enough of an immune response to justify moving on with human trials.
2) Phase I Study – After a promising animal test, the process moves to what is referred to as clinical trials, meaning testing in human subjects. The first step in this process is a Phase I study, which is the first setting in which an experimental vaccine is given to people. The trial, which can last up to 2 years, may enroll between 20 to 100 volunteers. A Phase I study primarily seeks information on safety, particularly looking for any vaccine-related side effects. The study can also provide data on the dose and administration schedule needed to achieve the optimal immune responses.
3) Phase II Study – Once Phase I studies show the experimental vaccine is safe, well tolerated, and appears promising, it can advance into Phase II. These studies, which can last longer than 2 years, enroll between 100 to 300 volunteers. In these studies researchers gather more data on safety and immunogenicity. These studies also test the effects of varying the doses, and are also referred to as dose-ranging studies.
4) Phase III Study – The most promising vaccine candidates move into Phase III, enrolling 10,000 or more people. A Phase III study, 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.
An intermediary study, called a Phase IIb study is being considered, as a middle step between the Phase II and the Phase III studies. This study would enroll between 2,000 and 9,000 volunteers. It appears, as of the time of writing, that Phase IIb studies are not a requirement like the others.
Besides the required tests, the FDA may require additional testing and data at any point. Furthermore, the proposed manufacturing facility undergoes a pre-approval inspection during which production of the vaccine as it is in progress is examined in detail. Vaccine approval also requires the provision of adequate product labeling to allow health care providers to understand the vaccine’s proper use, including its potential benefits and risks, to communicate with patients and parents, and to safely deliver the vaccine to the public.
Until a vaccine is given to the general population, all potential adverse events cannot be anticipated. Thus, many vaccines undergo Phase 4 studies-formal studies on a vaccine once it is on the market. Also, the government relies on the Vaccine Adverse Event Reporting System (VAERS) to identify problems after marketing begins. The VAERS system and how it works is discussed further on this website.