The Trump administration is pushing to have hundreds of millions of doses of a COVID-19 vaccine available by the end of the year. However, experts say the unprecedented speed risks taking shortcuts on safety, and there's no guarantee that any of the vaccine candidates will work.
Eight contenders are at the front of the pack.
These eight vaccine candidates are undergoing human testing in clinics in China, the United States, Britain and Germany. Behind them are at least 94 others in various stages of development.
But an effective vaccine might not protect against a mutated virus.
