What does it take for a vaccine to be approved?

What does it take for a vaccine to be approved, produced and marketed

     Prior to the FDA approval of vaccines they are tested extensively by scientists to be effective and safe.  Scientists say vaccines are the best defense we have against fighting infectious diseases; however no vaccine if 100% safe or effective.  Differences in our immune systems can cause reactions which sometimes lead to injuring a person.  The topic of vaccine safety is always a parents concern. 

     Vaccine licensing takes up to 10 years or longer.  The FDA requires vaccines to undergo three clinical trials with human subjects as a part of the licensing criteria. The first of the clinical trials will usually last only a few months and are with a very small group of people anywhere from 20 to 100 volunteers. This phase of the trial is to evaluate basic safety and identify common side effects.  The second trial will last for several months to two years with several hundred volunteers.  This period of the trial is used for the composition of the vaccine as to how much of the vaccine is needed , the correct dosage and any side effects.  If the vaccine is found to be ineffective or causing serious side effects the trial stops at this point.  If everything looks good up to this point the third trial will proceed. This period will last for several years involving hundreds to several thousand people.  If the vaccine trial  goes well then the manufacture will apply to the FDA for licensing, one for the vaccine and one for the production of where the product will be made.