Which statement best explains why the influenza vaccine must be updated every year?

Question

1 point
Some years, the influenza vaccine is not as strong as in others.
Some years, the influenza vaccine kills the virus, while in other years it does not.
The influenza virus adapts and mutates every year, so new vaccines must be produced.
The influenza vaccine does not necessarily stimulate the immune system to produce antigens.

Answer 1

The influenza virus adapts and mutates every year, so new vaccines must be produced.