Question

Why must a new flu vaccine be manufactured annually?

Se*ual reproduction between flu viruses creates new strains.

The genes for the proteins on the exterior of the flu virus mutate frequently.

The flu causes mutations in the host cell DNA.

The flu virus develops methods to break down the vaccine.

Answer 1

D or A

But I do know...

It's because new strains of the virus are constantly appearing and evolving, so the vaccine must change along with them.