Soledad im soledad obrien. Welcome to matter of fact. How will the covid 19 pandemic end . The most certain way would be the development of a safe and effective vaccine. Private companies and governments worldwide are racing to produce a vaccine by the end of the year. But doctor anthony fauci, the countrys top Infectious Disease expert said it could take 12 to 18 months. And even that timeline would be ambitious by historical standards. There are roughly 100 candidates for a vaccine in the works, with a handful fasttracked for human trials. The Clinical Development of a Vaccine Development has three phases. First, its given to a small group of people, then a bigger group, then an even bigger group, in order to test if its safe and effective. And these series of tests can take years, which has led to calls for a different type of testing. Our special contributor joie chen looks at the push for human challenge trials. Josh my names Josh Morrison. Im a volunteer for human challenge trial