A 13-year-old girl in British Columbia who was hospitalized with bird flu for several weeks late last year harbored a mutated ...

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.

As the seasonal flu picks up, there are even more opportunities for the bird flu to acquire mutations as the different influenza viruses mix. A 13-year-old girl in British Columbia who was ...