They said it couldn't be done: a vaccine developed in record time. In 1967, Merck had a license for a mumps vaccine, less than five years for work that normally takes decades. But that record is now being shattered as the COVID-19 vaccine reaches the market in less than a year. It's an unprecedented scientific development in a whirlwind year of crisis.

Watch the GZERO World episode: A Shot in the Arm: Moderna's Co-Founder on the COVID-19 Vaccine