Norovirus, often erroneously called the "stomach flu," sickens an estimated 21 million Americans and 685 million people worldwide every year, and though there is currently no preventive vaccine, a promising contender is in the works.

Norovirus is surging across the U.S., with case numbers higher now than they've been at the same time in more than a decade, according to the U.S. Centers for Disease Control and Prevention (CDC). There is no antiviral treatment for the miserable but thankfully short-lived illness,