Vaccines help protect us from many diseases, but have you ever wondered what it takes to get a vital new vaccine to market?

It's a rigorous testing and approval process. The basic steps:

1. Exploratory and preclinical research. In the earliest stages of development, lab scientists conduct basic research—they begin to explore the feasibility of a new vaccine. A candidate vaccine may then be studied in cell or tissue cultures and in animals but not yet in humans.

2. Clinical trials. Next, if allowed by the U.S. Food and Drug Administration (FDA), a promising vaccine may be studied in people. Among other things, scientists will assess the vaccine's safety and ability to provide immunity, the number of doses needed, and any side effects.

Most clinical trials happen in three phases:

• Phase 1. The vaccine is given to a small group of adult volunteers. (Later, children also may get the trial vaccine, if it is intended for them, after it is first tested in adults.)

• Phase 2. The vaccine is given to hundreds of people, and some of the participants are similar to those for whom the new vaccine is intended. These trials are randomized and well controlled and include a placebo group.

• Phase 3. The vaccine is given to thousands of people and compared to a placebo. The trials are randomized and double blind—neither the trial participants nor the health officials know which participants are receiving the vaccine and which are getting the placebo.

3. A new vaccine is ready. Once the clinical studies are complete, a successful candidate vaccine may be licensed for use if found to be safe and effective and if its benefits outweigh its side effects.

4. Ongoing monitoring. Even after a new vaccine is licensed, FDA will continue to monitor it for safety—a kind of quality assurance process. This includes periodic inspections of the vaccine maker's production facilities. In addition, FDA and the Centers for Disease Control and Prevention track side effects linked to the new vaccine that get reported by individuals, doctors and others.

Vaccines can take several years to develop. But, as we've seen with efforts to develop a coronavirus vaccine, the process can sometimes be fast-tracked.