Have you ever wondered why you have to get a flu shot every year, but some vaccines are one-and-done? It all has to do with how and how fast viruses evolve - and that depends on mutation rates.

It's dusk in central Bangladesh, in a community within the district of Faridpur. A 50-year-old man sits outside his home beside a rice paddy. His name is Khokon. A fiery beard, dyed a bright orange, ...

Some viruses mutate more rapidly than others. Learn more about why that is and what that means for your health. Have you ever wondered why you have to get a flu shot every year, but some vaccines are ...