Don't worry ! You will NOT derail any of your marathon training efforts because you have to take a week or so off from your running routine. The flu is SERIOUS this season. Take care of yourself.
Here's the thing, you do not want to run while you are sick. It wouldn't be a productive workout and your risk for injury increases when you try to push your body too soon. Take a few days off. Honestly, you will not ruin your efforts at running the Boston Marathon if you miss a week of runs.
Take the time you need to get over this flu. And yes, that might mean two weeks of not running. Keep drinking your fluids and get plenty of REST. Don't try to start running too soon or you'll risk getting sick all over again. Right now, your body needs energy to fight the flu instead of for exercise.