Whenever you can. It's not always to prevent you from getting the flu, but to prevent you from passing it along to others that can't take a flu vaccine for what

Whenever you can. It's not always to prevent you from getting the flu, but to prevent you from passing it along to others that can't take a flu vaccine for whatever reason. Also elderly, children, immunocompromised folks. You might have the flu and not know it and it could be deadly to someone else.