If a vaccine protects you for most of your life against a particular pathogen, why do you need a new flu shot every year? A. Influenza evolves very quickly and its antigens mutate so that your memory cells from the last vaccine won’t recognize it. B. Influenza is so strong that you need a booster every year to make sure your body can fight it. C. Influenza is a virus, and vaccines only generate memory cells for bacterial infections. D. You don’t need it every year, it is just offered every year for anyone who does not have it yet.

If you got a flu shot this year, next year you'll need it again.

Explanation:

This is because the virus changes, usually rendering the previous year's vaccine partly or totally useless. hope this helps you :)

a physical change is being made.

unicellular organisms, like bacteria, are able to perform all life functions within one single cell. multicellular organisms need many different types of cells to carry out the same life processes. each of these special types of cells has a different structure that it perform a specific function.