The only negatives about getting a flu shot, besides the contraindications noted above, is that is not a 100% guarantee that you will not get the flu after receiving a flu shot, and you may experience some sore soreness in the injection site and other mild flu-like symptoms for a day or two after getting vaccinated. It takes up to two weeks for your body to develop immunity to the seasonal influenza strand. As a result, if you contracted the flu during those two weeks, your immunity may not be strong enough to prevent you from getting sick. However, these symptoms are usually mild and nothing to worry about, as the vaccine will give your body an added boost in fighting off any flu infection you get.